ELEMENTARY 
HOUSEHOLD  CHEMISTRY 


THE  MACMILLAN  COMPANY 

NEW  YORK  •    BOSTON   •    CHICAGO  •   DALLAS 
ATLANTA  •    SAN   FRANCISCO 

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THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


ELEMENTARY 
HOUSEHOLD  CHEMISTRY 

AN    INTRODUCTORY  TEXTBOOK   FOR 
STUDENTS  OF  HOME  ECONOMICS 


BY 


JOHN    FERGUSON   SNELL 

PROFESSOR  OF  CHEMISTRY,  MACDONALD  COLLEGE 
MCGILL  UNIVERSITY 


ETefo  gorfc 

THE   MACMILLAN   COMPANY 
1914 

AK  rights  reserved 


COPYRIGHT,  1914, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  June,  1914.     Reprinted 
September,  1914. 


»  * »  »i  •••;  €••••••    *    .    •*. 

'<  *  +• '  **•*.*••  j   r  .**     r 


Nnrfaoob 

J.  8.  Gushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

THE  recent  development  of  courses  of  instruction  in  Home 
Economics  in  America  has  created  a  field  for  textbooks  pre- 
pared to  meet  the  special  needs  of  this  new  class  of  students. 
The  course  in  chemistry  presented  in  this  book  is  the  outcome 
of  several  years'  experience  with  a  class  of  students,  the  ma- 
jority of  whom  have  had  no  previous  instruction  in  the  science. 
The  text  has  been  written  with  the  needs  of  such  students 
primarily  in  mind,  but  the  hope  is  entertained  that,  with  suit- 
able omissions,  it  may  also  be  found  useful  in  the  many  insti- 
tutions in  which  the  student  of  household  chemistry  approaches 
the  subject  after  a  preliminary  training  in  general  chemistry. 
The  principle  which  has  been  kept  constantly  in  mind  is  to 
introduce  the  applications  of  chemistry  to  household  affairs  as 
early  and  as  often  as  possible  and  to  present  only  such  por- 
tions of  the  subject  matter  of  theoretical  chemistry  as  is 
essential  to  the  comprehension  of  these  applications.  In  this 
way  the  student's  interest  is  enlisted  and  maintained  —  a  most 
important  consideration  in  the  teaching  of  an  applied  science. 

The  author's  thanks  are  due  to  the  many  friends  who  have 
taken  an  interest  in  the  preparation  of  this  volume  and  more 
particularly  to  Professor  John  Bonsall  Porter  of  McGill  Uni- 
versity ;  Mr.  F.  O.  Farey,  of  the  Robert  W.  Hunt  Company, 
Montreal ;  and  Mr.  Peter  H.  Walsh,  Chemist  of  the  Dominion 
Textile  Company,  Magog,  Quebec,  for  suggestions  in  regard 
to  the  chapters  on  fuels,  soaps,  and  textiles,  respectively ;  to 
Miss  Katharine  A.  Fisher,  Head  of  the  Household  Science 
Department,  Macdonald  College,  for  the  table  of  weights  of 
one  cupful  of  various  food  materials ;  and  to  Professor  H.  C. 
Sherman,  of  Columbia  University,  for  numerous  suggestions. 


vi  PREFACE 

For  permission  to  use  illustrations  the  author  desires  to  make 
acknowledgments  to  Misses  Kinne  and  Cooley,  authors  of 
"Shelter  and  Clothing";  to  Sir  William  Ramsay;  to  Pro- 
fessor R.  H.  Richards,  and  Mrs.  W.  O.  Atwater  ;  to  Messrs. 
Eimer  and  Amend,  New  York ;  to  the  Niagara  Electrochemi- 
cal Company ;  and  to  the  publishers. 

J.   F.   SNELL. 

MACDONALD  COLLEGE, 
January  I,  1914. 


CONTENTS 


CHAPTER 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 
X. 

XI. 
XII. 


^   XVI. 
VXVII. 

r 

XVIII. 

XIX. 

XX. 

XXI. 

XXII. 

XXIII. 

XXIV. 

XXV. 


PAGE 

THE  SUBJECT  MATTER  OF  CHEMISTRY.        .        .  1 

DECOMPOSITION  AND  COMBINATION      ....      11 

ELEMENTS        .        ......        .        .18 

COMPOUNDS     .        .        .        .        .        .        .        .        .22 

CHEMICAL  NOTATION     .        .        ...  26 

THE  ATOMIC  THEORY    .......      28 

THE  LAW  OF  DEFINITE  PROPORTIONS  .        .        .        .      34 

COMPOUNDS  OF  THE  SAME  ELEMENTS  IN  DIFFERENT 

PROPORTIONS    .......        .38 

COMBUSTION    .        .        .        .        .        .        .        .        .41 

THE  RELATION  OF  COMBUSTION  TO  HEAT  ...      51 
FUELS       .  ........      59 

FUELS  (Continued}  .        .        .        .        .        .        .66 

LIGHT  AND  ILLUMINANTS      .        .        .        .        .        .72 

ACIDS  AND  SALTS  ........      82 

ALKALIES         .........      91 

BASES  AND  BASIC  OXIDES      .        .        .        .  .94 

REACTIONS  OF  ACIDS  WITH  BASES  AND  WITH  BASIC 

OXIDES.     IONIZATION      ......      98 

METAL  TARNISHES  ........     105 

IRON  RUST      .........     109 

STRONG  AND  WEAK  ACIDS  AND  BASES         ...     114 
HYDROLYSIS  OF  SALTS   .......     117 

HARD  WATER          ........     121 

AMMONIA  AND  THE  AMMONIUM  RADICLE  .  .  .  127 
ORGANIC  RADICLES.  HYDROCARBONS  AND  ALCOHOLS  132 
ESTERS,  FATS  .  138 


Vlll 


CONTENTS 


CHAPTER 

XXVI. 

XXVII. 

XXVIII. 

xxix. 

XXX. 


^-  XXXI. 

XXXII. 

XXXIII. 

XXXIV. 

XXXV. 

XXXVI. 

XXXVIL 

XXXVIII. 

XXXIX. 

XL. 

XLI. 

XLIL 
VXLIII. 


PAGE 

HYDROLYSIS  OF  ESTERS.     SAPONIFICATION     .        .     143 
COMMERCIAL  SOAPS  .  148 


FOREIGN  INGREDIENTS  OF  COMMERCIAL  SOAPS     . 
SPECIAL  SOAPS  AND  SCOURING  POWDERS 
SOLUTION  AND   EMULSIFICATION   OF   FATS.     THE 

CLEANING  OF  FABRICS  .  ... 
THE  GENERAL  COMPOSITION  OF  FOODS. 
THE  CARBOHYDRATES.  I  .  ...  . 

THE  CARBOHYDRATES.     II 

THE  PROTEINS.     I     .        .        . 

THE  PROTEINS.     II  .        .        .        .        . 

THE  FUNCTIONS  OF  FOOD        ..... 

THE  DIGESTION  OF  FOOD        .        .        .        .        . 

FOODS  OF  VEGETABLE  ORIGIN 

FOODS  OF  ANIMAL  ORIGIN 

TEXTILE  FIBERS  OF  ANIMAL  ORIGIN.     WOOL  AND 

SILK 

TEXTILE  FIBERS  OF  VEGETABLE  ORIGIN.     COTTON, 

LINEN,  AND  ARTIFICIAL  SILK. 
BLEACHING  AND  BLUEING        ...        .        , 
DYEING -    .        .        . 


APPENDIX  A.  —  TABLES  OF  COMPOSITION  OF  FOODS 
APPENDIX  B.  —  REAGENTS  .  .  .  .  .  , 
APPENDIX  C.  —  THE  METRIC  SYSTEM.  .  . 


151 

155 

158 
162 
166 
173 
182 
188 
192 
201 
207 
213 

218 

229 
243 
254 

267 
288 
294 


LIST    OF    PLATES 


Ellen  Henrietta  Swallow  (Mrs.  Richards)  i 

Robert  Boyle  .         . 18 

Jons  Jakob  Berzelius        .         .         .         .         .         .  26 

John  Dalton 28 

John  Mayow 42 

Joseph  Priestley 44 

Antoine-Laurent  Lavoisier       .         .         ...         .         .         .46 

Benjamin  Thompson  (Count  Rumford)   .....       52 

Joseph  Black 92 

Svante  August  Arrhenius 98 

Emil  Fischer 182 

Wilbur  Olin  At  water 192 

The  Atwater-Rosa  Respiration  Calorimeter  .  .  .  ^  .194 
The  Atwater-Rosa-Benedict  Respiration  Calorimeter  .  .196 
Textile  Fibers,  magnified 218 


ELLEN  HENRIETTA  SWALLOW. 
MRS.  ROBERT  HALLOWELL  RICHARDS.— 1842-1911. 

Trained  as  a  chemist,  and  engaged  up  to  the  time  of  her  death  in  the  teaching 
of  chemistry,  Mrs.  Ellen  H.  Richards  became  one  of  the  foremost  leaders  in  the 
application  of  scientific  principles  to  the  management  of  the  household. 


ELEMENTARY  HOUSEHOLD 
CHEMISTRY 

CHAPTER  I 
THE   SUBJECT   MATTER   OF  CHEMISTRY 

CHEMISTRY  is  a  science.  The  word  science  is  derived  from 
a  Latin  word,  scire,  meaning  "  to  know."  Science  and  knowl- 
edge are  therefore  closely  related  words.  Science  is  knowl- 
edge. But  the  term  science  is  applied  only  to  such  knowledge 
as  is  based  upon  careful  and  accurate  observations  and 
correct  reasoning  thereupon.  A  man  might  gain  a  rough 
knowledge  of  the  distance  between  Montreal  and  New  York 
by  recalling  that  his  grandfather  had  walked  from  the  one 
city  to  the  other  in  two  weeks'  time,  and  observing  that  he 
himself  could  walk  twenty-five  miles  a  day.  Such  knowl- 
edge would  be  unscientific.  In  contrast  with  it  we  have 
represented  in  our  maps  and  geographical  books  the  scientific 
statement  of  the  distance  between  the  two  cities,  based  upon 
painstaking  measurements  or  "surveys." 

In  building  up  science  we  make  much  use  of  experiment ; 
that  is,  we  arrange  that  the  conditions  under  which  we  make 
our  observations  shall  be  as  favorable  as  possible  to  accu- 
racy and  to  the  drawing  of  correct  conclusions.  The  man 
who  wished  to  know  the  distance  from  New  York  to  Montreal 
could  obtain  a  more  accurate  estimate  by  making  the  journey 
himself  on  foot,  taking  care  to  maintain  a  uniform  pace  and 
to  walk  the  same  number  of  hours  each  day,  than  by  relying 
upon  his  recollection  of  his  grandfather's  account  of  the  time 


£.;„'..  .  £1  EKKNTAI^Y. HOUSEHOLD  CHEMISTRY 


required  for  the  journey.  The  former  would  be  an  experi- 
mental determination  of  the  distance.  The  professional  sur- 
veyor's measurement  is  also  an  experimental  one,  but  the 
conditions  of  observation  are  much  more  carefully  controlled, 
and  the  correctness  of  the  measurements  is  checked  in  many 
different  ways,  all  depending  upon  experiments. 

Chemistry  is  only  a  branch  of  science.  That  is  to  say,  it 
is  the  body  of  knowledge  of  a  particular  class  of  phenomena 
which  the  human  race  has  been  able  to  acquire  by  such 
carefully  conducted  experimental  observations  and  such  logi- 
cal deductions  as  we  have  referred  to  above;  To  understand 
what  chemistry  is,  it  is,  therefore,  necessary  that  we  should 
get  a  clear  conception  of  the  kind  of  phenomena  (changes)  to 
which  this  science  relates.  And  it  is  fitting  that  this  clear 
conception  should  be  gained  through  the  use  of  experiments. 
In  making  experiments  the  student  should  bear  in  mind  that 
the  basis  of  all  science  is  careful  observation.  She  should 
therefore  examine  closely  every  material  used  and  every  stage 
of  the  experiment,  so  as  to  get  as  clear  and  full  a  knowledge 
as  possible  of  what  is  going  on  under  her  eyes. 

A  written  record  should  be  made  of  every  experiment, 
and  this  record  should  always  be  in  the  fol- 
lowing order : 

1.  What  I  did. 

2.  What  I  observed    (i.e.   saw,   smelled, 

tasted,  heard,  or  felt). 

3.  What  I  concluded  from  my  observa- 

tions. 
The  knowledge  that  one  has  to  record  an 

FlG   j Bunsen    experiment  always  of  itself  conduces  to  more 

burner.     Ordi-    careful  observation  and  reasoning. 

nary   form   for 

use  with  coal  Experiment  T.  The  Bunsen  Burner.  —  Un- 
screw and  examine  your  gas  burner.  Make  a 
sketch  of  the  burner  and  indicate  upon  it  where  the  gas  enters 
and  where  the  air  enters.  Learn  how  the  supply  of  each  is  in- 


THE    SUBJECT    MATTER    OF    CHEMISTRY 


creased  and  diminished.  Close  the  air  holes.  Turn  on  and  light 
"the  gas  and  note  the  appearance  of  the  flame.  Hold  a  cold  por- 
celain dish  in  the  flame.  Is  soot  deposited  ?  Gradually  open  the 
air  holes  and  note  the  effect  on  the  flame.  Prac- 
tice lighting  the  burner  with  the  air  holes  closed, 
and  then  regulating  the  supply  of  air  and  gas 
until  you  can  readily  obtain  a  good  non-luminous 
(blue)  flame.  Determine  whether  such  a  flame 
deposits  soot  on  the  cold  porcelain. 


FIG.  2.  —  Tirrill 
burner.  A  mod- 
ification of  the 
Bunsen  burner 
suitable  for 
gasoline  gas, 
as  well  as  for 
coal  gas. 


Experiment  2. 

Materials: 

Magnesium  ribbon  in  £-inch  pieces. 
Platinum  wire. 
Iron  nail. 

Asbestos  paper  or  light   asbestos   board,    2 
inches  X  i  inch,  previously  ignited  to  de- 
stroy organic  matter. 
Paper  in  pieces  2  inches  X  J  inch. 
File. 

Crucible  tongs  or  forceps. 

(i)  Bring  into    the    Bunsen    (non-luminous) 

flame  a  piece  of  magnesium  ribbon,  held  in  a  pair  of  forceps 

or  crucible  tongs.     Describe  what  occurs.     Examine  the 

product.     Is  it  magnesium? 
In  what  respects  does  it  dif- 
fer from  magnesium  ? 
(2)  Bring  a  piece  of  platinum 
into  the  flame.      Note  the 
changes  of  color  as  it  be- 
comes hot.     Allow  to  cool. 
Is  it  still  platinum  ? 
In  the  same  manner  heat  (3) 
an  iron  nail,  (4)  a  piece  of 
asbestos,     (5)     a    piece    of 
paper. 
Note  appearance  of  each,  (a)  while  it  is  in  the  flame,  (b)  after 

it  has  cooled  again. 

Write  in  one  column  the  names  of  those  substances  which  are 
the  same  at  the  end  of  your  experiment  as  at  the  beginning,  and 
in  another  column  those  which  have  been  changed  into  something 
different.  The  former  suffered  physical  changes  during  the  heat- 


FIG.  3.  —  Breaking  a  piece  of  glass 
tubing.  Make  a  scratch  on  one 
side  of  the  tubing  with  a  single 
stroke  of  the  file.  Place  the 
thumbs  on  the  other  side  of  the 
tubing,  directly  opposite  the  file 
mark.  Grasp  the  tubing  with 
the  thumbs  and  press  backwards 
towards  the  thumbs. 


4  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

ing,  the  latter  chemical  changes.  Note  that  iron  will  be  classed 
differently,  according  as  you  consider  (a)  the  outer  surface  or 
(&)  the  interior  as  disclosed  by  filing  off  the  surface. 

Experiment  3.* 

Materials: 

An  accumulator  or  any  type  of  primary  cell. 
A  wire  resistance. 
A  mounted  magnetic  needle. 

Connect  the  two  poles  of  a  voltaic  cell  through  a  resistance. 
Bring  a  magnetic  needle  near  the  connecting  wire.  What  occurs  ? 
Break  and  remake  the  connection.  Does  the  needle  undergo  a 
physical  or  a  chemical  change  when  brought  near  the  wires  ? 

Experiment  4. 

Materials : 

Glass  tubing,  about  6  mm.  diameter.1 
File. 

Cut  off  a  piece  of  glass  tubing  about  15  cm.  (6  in.)  long.  Heat 
the  middle  of  the  piece  of  tubing  in  the  Bunsen  flame,  rotating  it 

constantly.  When  it  is  quite  soft, 
remove  from  flame,  draw  out  to 
a  small  thread,  and  fuse  off  the 
thread  in  the  flame,  forming  two 
small  tubes  closed  at  one  end. 
Heat  the  closed  end  of  each  of 

FIG.  4.— Drawing  out  glass  tubing.  these  tubes  in  the  flame>  rotating 

The  glass  is  held  above  the  inner  constantly,  and  when  quite  soft, 

cone  of  the  flame  and  is  constantly  remove  from  flame  and  blow  into 

rotated    until    soft.     Just  before  th  d     f  th     tub       SQ  as 

drawing,  it  is  removed  from  the  ' 

flame  to  round  out  the  glass.     It  may 

either   be    rounded    off,  forming 

simply  a  closed  tube  (Fig.  6),  or  blown  into  a  bulb,  forming  a  matrass 
(Fig.  7). 


FIG.  5.  —  Glass  tubing  drawn  out. 

In  what  respects  does  the  sealed  tube  differ  from  the  original  ? 
Is  it  still  glass  ?    In  what  respects  does  hot  glass  differ  from  cold  ? 

*  All  experiments  marked  by  the  asterisk  are  recommended  for  demonstration 
by  the  teacher  rather  than  for  performance  by  the  individual  student. 
1  See  Tables  of  Metric  System,  p.  294. 


THE    SUBJECT    MATTER    OF    CHEMISTRY 


Are  hot  glass  and  cold  glass  different  substances?    Does  glass 
suffer  a  physical  or  a   chemical    change   during 
heating  ?    Does  hot  glass  suffer  phys- 
ical or  chemical  changes  when  drawn 
out,  and  when  blown  ? 

Keep  the  matrass  or  sealed  tube  for 
use  in  a  later  experiment. 


FIG.  7.  —  A 
matrass. 


FIG.  6.  —  Glass 
tube  closed  at 
one  end.  The 
narrow  thread 
of  glass  (Fig. 
5)  is  melted 
and  drawn  off. 
The  end  of  the 
tube  is  then 
softened  in  the 
flame,  and,  by 
blowing,  either 
rounded  off  or 
expanded  into 
the  bulb  of  a 
matrass  (Fig. 
7). 


Experiment  5. 

,    ^  Materials : 

( )  Compressed  yeast,  £  cake. 

Solid  commercial  grape  sugar 
("glucose"  or  "dextrose"), 
2.5  grams. 

Dissolve  2.5  grams  glucose  in  20  cc.  water.  Rub 
up  a  little  yeast  (\  cake  or 
less)  with  5  cc.  water.  Add  it 
to  the  glucose  solution,  and 
allow  to  stand  two  or  three 
hours  in  a  test  tube  in  a  warm 
part  of  the  laboratory.  The 
effervescence  (bubbling)  ob- 
served is  caused  by  the  forma- 
tion of  a  gas  (carbonic  acid  gas) 
which  has  the  property  of  turning  limewater 
milky.  To  test  for  the  gas,  dip  a  glass  loop 
(Fig.  9)  into  limewater  (calcium 
hydroxide)  solution,  and  hold  the 
film  of  liquid  in  the  test  tube 
above  the  glucose  solution  for 
about  half  a  minute.  Then  look 
through  the  film  towards  the  light. 
The  test  is  obtained  more  promptly 
if  the  test  tube  has  been  loosely 
covered  for  a  few  minutes. 

The  chemical  change  illustrated 
in  this  experiment  occurs  in  the 
common  fermentation  of  fruit  juices  (which  con- 
tain glucose).  Besides  the  carbonic  acid,  alco- 
hol is  formed.  While  the  carbonic  acid  gas 
escapes,  the  alcohol  remains  in  the  liquid  and 
the  fruit  juices  become  wines,  ciders,  etc. 


FIG.  g.  —  Glass  loop 
for  limewater  films. 
This  can  be  made 
from  a  piece  of 
small  (2  to  4 
millimeter)  glass 
tubing  by  soften- 
ing in  the  flame, 
drawing  out,  and 
quickly  turning 
the  soft  glass 
thread  back  upon 
itself.  The  loop 
should  be  about 
S  to  7  millimeters 
long  and  2  to  3 
millimeters  wide. 


FIG.  8.  —  A 
test  tube. 


6  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Experiment  6. 

Materials : 
Common  salt. 

Silver  nitrate  —  a  solution  and  also  a  specimen  of  the  solid 
substance. 

Dissolve  the  salt  in  water  in  a  test  tube.  The  silver  nitrate 
reagent  has  been  made  similarly  by  dissolving  solid  silver  nitrate 
in  water.  Note  that  both  solutions  are  clear.  Pour  a  little  of 
the  silver  nitrate  solution  into  the  salt  solution.  The  clouding 
which  appears  is  due  to  the  separation  of  innumerable  minute 
particles  of  a  substance  (silver  chloride)  which  does  not  dissolve 
in  water.  These  particles  are  in  the  solid  state.  To  verify 
this  close  the  test  tube  with  the  thumb  and  shake  vigorously, 
so  as  to  combine  the  particles  into  larger  ones.  A  solid  forming  in, 
and  separating  out  from,  a  liquid  is  called  a  precipitate.  In  this 
experiment  the  substance  silver  chloride  is  formed  as  a  precipitate 
when  salt  (sodium  chloride)  and  silver  nitrate  solutions  are  mixed. 
At  the  same  time  a  substance,  called  sodium  nitrate,  is  also  pro- 
duced, but  this  substance  being  soluble  in  water,  like  the  original 
substances,  does  not  make  itself  visible  in  the  experiment. 

Experiment  7. 

Materials : 

Milk. 

Fold  a  filter  and  fit  it  in  a  glass  funnel.  Pour  milk  upon  the 
filter.  Does  it  pass  through  the  filter  unchanged?  Add  a  few 


FIG.  10. — Folding  a  filter.      FIG.  u.  —  Foiling  a  filter.       FIG.  12.  —  Folding 
First  stage.  Second  stage.  a  filter.      Third 

stage. 

drops  of  acetic  acid  to  the  milk,  and  again  pour  upon  the  filter. 
Has  the  acid  caused  a  chemical  change  in  the  milk  ? 


THE    SUBJECT    MATTER    OF    CHEMISTRY 


Experiment  8. 

Materials : 
Milk. 
Junket  tablets  or  rennin  solution. 

In  a  test  tube  surrounded  by  a  beaker  of  water,  heat  milk  to 
the  temperature  of  the  hand.  Add 
a  few  drops  of  rennin  solution  or  of 
an  aqueous  solution  of  junket  tab- 
lets (which  contain  rennin)  and 
mix.  Allow  to  stand  for  15  min- 
utes. Shake  the  test  tube  and  pour 
the  contents  on  a  filter.  Has  a 
chemical  change  occurred  in  the 
milk? 

Experiment  9.* 

Materials : 

Potassium  iodide  crystals. 
Mercuric    chloride    crystals 
(Poison!). 

Apparatus  :  FIG.  13.  —  A  filter  ready  for  use. 

Mortar  and  pestle. 

Rub  together  in  the  mortar  a  crystal  of  potassium  iodide  with 
one  of  mercuric  chloride.     What  evidence  appears  that  a  new 
substance  is  formed?    Actually  two  new  substances  are  formed, 
but  one  of  these  is  white  like  the  potas- 
sium iodide  and  mercuric  chloride. 

Experiment  10.* 

Dissolve  a  crystal  of  potassium  iodide 
in  water  in  a  test  tube.  In  another  tube 
dissolve  about  an  equal  quantity  of  mer- 
curic chloride.  Shaking  and  warming 
will  hasten  solution.  Pour  a  little  of  the 
potassium  iodide  solution  into  a  third 
test  tube,  and  gradually  add  mercuric  chloride  solution  to  it. 
The  red  precipitate  is  the  same  red  substance  that  was  formed  in 
Experiment  9.  The  white  substance,  referred  to  above  as  being 
formed  at  the  same  time,  is  in  solution  in  the  water. 

NOTE.     Directions  for  making  reagents  called  for  in  some  of  the  experiments 
in  this  and  other  chapters  will  be  found  in  Appendix  B. 


FIG.  14.  —  Mortar  and 
pestle. 


8 


ELEMENTARY    HOUSEHOLD    CHEMISTRY 


Experiment  u.* 

Add  the  remainder  of  the  potassium  iodide  solution  to  the  test 
tube  containing  the  red  precipitate  (Expt.  10).     Does  a  chemical 

change   occur?      What   is   the 
evidence  ? 

Experiment  12. 

Hold  a  cold,  dry  beaker, 
mouth  downward,  above  a 
Bunsen  flame  for  an  instant. 
Note  the  deposition  of  dew  — 
composed  of  minute  droplets  of 
water.  Close  the  beaker  with 
a  watch  glass,  invert  it,  pour  in 
a  little  limewater  and  shake. 
What  gas  was  present  in  the 
beaker?  (See  Expt.  5.) 

Repeat  this  experiment,  using 
an  unlighted  burner  with  the  gas 
flowing.  Is  any  dew  deposited  ? 
Is  the  gas  which  affects  lime 
water  present?  What  kind  of 
change  do  you  infer  to  be  in- 

volved  in  t 


EXERCISES 

1.  Make  a  tabular  summary  of   the  results  of  Experiments 
3-12,  putting  the  chemical  changes  into  one  column,  the  physical 
into  another. 

2.  Arrange-  the  following  changes  in  their  proper  columns  as 
(a)  chemical  or  (b)  physical : 

(a)  Breaking  stone. 

(6)  Passing  an  electric  current  through  a  copper  wire. 

(c)  Making  horseshoes  from  bar  iron. 

(d)  Making  wine  from  fruit  juice. 

(e)  Burning  wood. 

(/)   Milling  wheat,  i.e.  grinding  it  and  separating  the  flour  from 

the  bran, 
(g)  Ironing  linen. 
(ti)  Scorching  linen. 


THE    SUBJECT    MATTER    OF    CHEMISTRY  9 

(i)  Manufacturing  glass  from  sand,  soda,  and  lime. 

(/)  The  rusting  of  iron. 

(k)  The  growing  of  a  tree. 

(/)  The  assimilation  of  food  by  an  animal. 

All  the  changes  which  substances  undergo  in  the  pro- 
cesses of  nature  and  of  the  arts  may  be  divided  into  the  two 
classes  illustrated  by  the  above  experiments,  viz. : 

1.  Physical  changes,  in  which  no  new  substance  is  formed. 
Changes  in  state  of  motion,  such  as  that  involved  in  throw- 
ing or  catching  a  ball,  are  purely  physical.     So  also  are 
changes  in  form,  such  as  are  produced  by  cutting,  grinding, 
or  hammering.     Changes  in   temperature   and  changes  in 
electrical  condition  may  bring  about  chemical  changes,  but 
they  are  not  in  themselves  chemical. 

2.  Chemical  changes,  in  which  one  or  more  new  sub- 
stances   are    formed.     We    recognize    new    substances    by 
observing  such  physical  properties  as  color,  physical  state 
(solid,  liquid,  or  gaseous),  density  (weight  of  a  given  volume, 
"heaviness  "),  solubility  in  water  or  in  other  solvents,  etc. 
In  some  instances  it  is  difficult  to  decide  whether  a  new 
substance  has  been  formed  or  not.     But  in  many  others, 
as  we  have  seen  in  the  experiments,  the  product  of  the 
change  is  readily  recognized  as  a  new  substance. 

Chemistry  is  the  science  which  treats  of  those  changes 
or  "  reactions  "  in  which  new  substances  are  formed. 

Chemical  changes  seldom,  if  ever,  occur  without  the  accom- 
paniment of  physical  changes.  In  Experiment  2,  for  example, 
not  only  is  a  new  substance  formed  in  place  of  the  magne- 
sium, but  heat  and  light  are  given  out.  Again,  the  heat 
evolved  produces  an  upward  current  in  the  air,  and  some  of 
the  white,  solid  product  of  the  chemical  change  is  carried  up 
as  a  smoke.  There  are  thus  a  number  of  physical  changes 
occurring  concomitantly  with  the  chemical  change.  In 
studying  chemical  changes  we  cannot  ignore  these  concomi- 
tant physical  changes,  but  we  direct  our  attention  partic- 


10  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

ularly  to  the  question  whether  new  substances  have  been 
produced,  and,  if  so,  what  those  new  substances  are. 

It  must  not  be  thought,  however,  that  chemical  changes 
are  the  only  objects  of  study  in  the  science  of  Chemistry. 
The  science  includes  also  the  study  of  the  properties  of  sub- 
stances and  of  their  "  composition,"  a  term  which  will  be 
understood  when  the  next  three  chapters  have  been  read. 


CHAPTER  H 
DECOMPOSITION  AND   COMBINATION 

THE  following  experiments  illustrate  chemical  changes  of 
two  classes.  The  chief  point  to  be  studied  in  each  experi- 
ment is  the  alteration  in  the  number  of  substances  present. 

Experiment  13. 

Materials : 

Mercuric  oxide  (best  the  red  modification  prepared  by  igni- 
tion) . 

Matrass  or  glass  tube  closed  at  one  end,  prepared  in  Experi- 
ment 4. 

Splints  of  pine  or  other  soft  wood. 

Heat  mercuric  oxide  in  a  matrass  or  glass  tube  closed  at  one  end. 
Test  the  escaping  gas  with  a  glowing  splint.  Note  what  collects 
on  the  inner  surface  of  the  tube.  How  many  substances  were  put 
into  the  matrass?  How  many  new  substances  were  formed? 
Is  this  a  chemical  or  a  physical  change  ? 
The  gas  which  affects  the  splint  is  called  oxygen. 

Experiment  14. 

Materials : 

Potassium  chlorate. 
Splints. 

Heat  potassium  chlorate  in  a  test  tube  until  bubbling  ceases. 
Apply  a  glowing  splint  to  the  gas  escaping  during  the  bubbling. 
Determine  whether  the  sub- 
stance left  in  the  tube  is  potas- 
sium chlorate  or  not.  For  this 
purpose  not  only  may  the  effect 
of  heat  on  this  residual  sub- 
stance be  compared  with  that  on 
the  original  potassium  chlorate,  FlG"  l6'  ~  A  test  tube  Mder' 

but  also  a  portion  of  each  may  be  dissolved  separately  hi  water 
and  treated  with  silver  nitrate  solution. 

ii 


12 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


In  the  main  experiment  how  many  substances  were  put  into  the 
tube  to  be  heated  ?  How  many  new  substances  were  found  to  be 
formed  ? 

Experiment  15. 

Heat  a  little  sugar  (about  0.5  gram)  in  a  test  tube.    Note  what 

escapes  from  the  tube  and 
what  is  left  in  it.  Test  the 
escaping  gas  with  blue  lit- 
mus paper.  How  many 
substances  were  put  into 
the  tube?  Were  new  sub- 
stances formed?  How 
many  were  detected? 

Experiment  16.* 

Materials : 

Sulphuric  acid  solution, 

about  10  per  cent. 
Apparatus: 

Hofmann's    electrolysis 
apparatus    (Fig.    18) 
or   the    simpler    ap- 
paratus    represented 
in  Figure  17. 
3   accumulators    in 
series   (or  other  ap- 
propriate   source    of 
direct  current). 
With   the   Hofmann   ap- 
paratus  full  of  the   dilute 
sulphuric   acid   solution  up 
to  the  bottom  of  the  reser- 
voir (or  with  the  test  tubes 
of  the  simplified  apparatus 
full  of  the  acid  and  inverted 
in  the  beaker  of  acid)  con- 
nect the  battery  to  the  bind- 


FIG.  17.  —  A  simple  apparatus  for 
the  electrolysis  of  water. 


ing  posts  and  allow  the  current  to  pass  until  a  considerable  quantity 
of  gas  has  collected  in  each  branch  of  the  apparatus.  Note  that 
about  twice  as  much  gas  collects  in  one  branch  of  the  apparatus 
as  in  the  other.  Invert  a  small  test  tube  over  one  of  the  outlet 


DECOMPOSITION    AND    COMBINATION 


tips,  open  the  cock,  and  allow  the  gas  to  escape  into  the  test 
tube.  Cover  the  tube  with  the  thumb,  invert,  and  immediately 
apply  a  flaming  splint.  Make  the  same  test  upon  the  gas  from 
the  other  limb  of  the  apparatus.  Also  test  each  with  a  splint 
with  a  glowing,  but  not  flaming,  end.  Compare  the  behavior  of 
the  two  gases.  One  of  these  gases  is  the  substance  already 
met  with  in  Experiments  13  and  14.  What 
is  its  name  ?  The  other  is  hydrogen.  Which 
of  the  gases  is  obtained  in  the  larger  quan- 
tity? Careful  experiments  have  shown  that 
none  of  the  sulphuric  acid  is  used  up  in  this 
experiment.  Indeed,  several  other  substances 
can  be  substituted  for  the  sulphuric  acid  with- 
out altering  the  result.  The  amount  of  water 
in  the  apparatus  is,  however,  a  little  less  after 
the  experiment  than  before.  The  diminution 
of  the  quantity  of  water  is  not  visible,  unless 
the  current  has  been  passed  for  some  hours. 
But  it  has  been  found  by  accurate  measure- 
ment that  the  water  lost  weighs  exactly  the 
same  as  the  sum  of  the  weights  of  the  hydro- 
gen and  oxygen  produced.  The  use  of  the 
sulphuric  acid  is  to  make  the  water  a  better 
conductor  of  electricity.  Pure  water  con- 
ducts electricity  so  badly  that,  using  it,  we 
should  require  years  to  obtain  as  much  gas 
as  we  do  in  a  few  minutes  with  the  mixture 
of  sulphuric  acid  and  water. 

If  the  hydrogen  and  oxygen  produced  in 
the  electrolysis  of  water  are  both  collected 
and  mixed  and  set  on  fire,  an  explosion  takes 
place,  and  if  the  experiment  is  conducted  in 
a  closed  apparatus  strong  enough  to  stand 
the  shock  of  the  explosion,  there  is  found  in  the  apparatus  after 
the  explosion  a  quantity  of  water  weighing  just  the  same  as  the 
hydrogen  and  oxygen,  and  therefore  just  the  same  as  the  water 
which  was  destroyed  by  the  electrolysis  that  produced  the  hydro- 
gen and  oxygen. 

Experiment  17.* 

In  a  hard-glass  test  tube  fitted  with  a  cork  and  bent  delivery 
tube  and  supported  in  a  clamp  on  a  ring  stand  heat  a  piece  of 


FIG.  1 8.  —  Hofmann's 
apparatus  for  the  elec- 
trolysis of  water. 


14  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

marble  weighing  from  2  to  5  grams.  A  large  Bunsen  or  a  Teclu 
or  Meker  burner  should  be  used.  Immerse  the  lower  end  of  the 
delivery  tube  in  limewater,  contained  in  a  small  test  tube.  Con- 
tinue to  heat  for  several  minutes  and  note  the  continued  slow 
evolution  of  gas  and  the  effect  of  the  gas  on  limewater. 

To  hasten  the  action  transfer  to  a  porcelain  crucible  the  marble 
remaining  in  the  test  tube  and  heat  in  the  flame  of  a  blast  lamp 
for  15  to  30  minutes.  Allow  to  cool  and  examine  the  residue.  Add 
to  it  as  much  warm  water  as  it  will  absorb  and  allow  it  to  stand 
a  few  minutes.  Add  more  water  to  the  product  and  test  the  water 
with  litmus  paper. 

The  material  of  which  marble  consists  is  known  in  chemistry 
as  calcium  carbonate.  The  gas,  which  it  evolves  on  heating  and 
which  affects  the  limewater,  is  called  carbon  dioxide,  and  the 
residue  left  in  the  crucible  after  all  the  carbon  dioxide  has  been 
driven  out  is  quicklime  or  calcium  oxide.  Quicklime  is  commonly 
made  from  limestone,  a  less  pure  calcium  carbonate  than  marble. 
Quicklime  and  water  react  to  form  slaked  (or  slacked)  lime,  and 
slaked  lime  dissolves  slightly  in  water,  yielding  limewater. 

The  student  will  have  observed  that  in  each  of  the  above 
experiments  (Nos.  13-17)  one  substance  is  converted  into 
two  or  more  new  substances.  Chemical  change  of  this  type 
is  called  decomposition.  Thus  we  say  that  the  red  solid, 
mercuric  oxide,  is  decomposed  by  heating  into  the  metallic 
liquid,  mercury,  and  the  colorless  gas,  oxygen;  and  that  water 
under  the  influence  of  an  electric  current  decomposes  into 
the  two  gases,  hydrogen  and  oxygen.  A  great  many  sub- 
stances are  decomposed  by  heating,  and  some  of  them, 
like  the  sugar  in  Experiment  15,  give  a  large  number  of  de- 
composition products.  A  great  many  also  are  decomposed 
by  the  electric  current,  and  a  special  name,  electrolysis,  is 
applied  to  decomposition  so  effected.  The  decomposition 
products,  we  say,  are  simpler  substances  than  those  from 
which  they  are  made.  Thus,  mercury  and  oxygen  are 
simpler  substances  than  mercuric  oxide;  and  potassium 
chloride  (the  white  residue  in  Expt.  14)  and  oxygen  are 
simpler  substances  than  potassium  chlorate. 


DECOMPOSITION   AND    COMBINATION  15 

In  many  instances  the  decomposition  products  can  be 
readily  recombined  into  the  original  substance.  For  instance, 
the  hydrogen  and  oxygen  obtained  from  water  in  Experiment 
1 6  can  be  recombined  into  water  by  simply  mixing  the 
gases  and  setting  the  mixture  on  fire.  We  are  therefore 
justified  in  regarding  the  more  complex  substances  as  com- 
pounds of  the  simpler.  Thus  we  say  that  mercuric  oxide 
is  composed  of  mercury  and  oxygen,  or  that  it  is  a  compound 
of  the  simpler  substances,  mercury  and  oxygen  —  although 
it  does  not  in  the  least  resemble  either  of  these  simpler 
substances ;  and  that  water  is  a  compound  of  hydrogen  and 
oxygen  (p.  13).  When  water  is  put  upon  hard  lumps  of 
quicklime  the  two  substances  combine,  forming  the  powdery 
substance  which  we  call  slaked  lime.  (See  Expt.  50,  p. 
96.) 

We  commonly  speak  of  the  decay  of  dead  animal  and 
vegetable  matter  as  "decomposition."  The  chemical  changes 
involved  in  such  decay  are  much  more  complex  than  any 
of  those  we  have  studied  in  our  experiments.  Every  animal 
or  vegetable  organism  comprises  a  great  many  different 
substances.  Even  the  parts  our  eyes  readily  recognize  as 
different  —  such  as  bone,  blood,  muscular  tissue  (flesh), 
and  fat  —  are  generally  mixtures  of  a  number  of  different 
substances.  And  very  commonly  substances  outside  of  the 
organisms,  particularly  water  and  air,  are  involved  in  the 
process  of  decay.  Nevertheless,  since  such  decay  does 
result  for  the  most  part  in  the  production  of  simpler  sub- 
stances than  those  originally  present  in  the  decaying  organ- 
ism, the  word  decomposition  as  applied  to  decay  has  a  signifi- 
cation closely  allied  to  our  definition  of  the  term. 

Chemical  change  which  results  in  the  formation  of  one 
substance  from  two  or  more  is  called  combination.  Com- 
bination has  already  been  illustrated  in  the  instance  of 
hydrogen  and  oxygen.  The  following  experiments  furnish 
further  illustrations  of  this  class  of  chemical  action. 


i6 


ELEMENTARY    HOUSEHOLD    CHEMISTRY 


Experiment  18. 

Materials : 
Roll  sulphur. 
Copper  foil,  i  inch  X  \  inch. 

Heat  a  little  roll  sulphur  to  boiling  in  a  test  tube.  While  the 
sulphur  is  actively  boiling,  drop  in  a  piece  of  copper  foil.  Note 
what  occurs.  The  great  majority  of  chemical  changes  are  accom- 
panied by  the  evolution  of  more  or  less  heat.  In  some,  the  heat 
is  so  great  as  to  make  the  solid  substances  involved  in  the  change 
give  out  light.  Many  of  the  chemical  reactions  which  produce 
great  quantities  of  heat  belong  to  the  class  we  are  now  considering, 
viz.  combinations.  (See  Expt.  19.) 


\ 

FIG.  19.  —  Burning  carbon  (charcoal)  in  a  current  of  oxygen.  The  oxygen  is 
generated  in  the  flask  by  heating  potassium  chlorate.  By  bubbling  through 
30  per  cent  potassium  hydroxide  in  the  first  wash  bottle,  it  is  freed  from 
any  carbon  dioxide  it  may  contain.  It  then  passes  through  the  heated 
glass  tube  containing  the  charcoal,  and  finally  through  the  second  wash 
bottle,  which  contains  limewater.  (Experiment  IQ.) 

Examine  the  product  formed  from  the  copper,  comparing  it  with 
the  original  copper  and  sulphur  as  regards  color,  cohesion,  etc. 
(Ordinarily  there  will  be  a  considerable  quantity  of  unchanged 
sulphur  left  in  the  test  tube,  but  this  is  readily  distinguished  from 
the  new  substance,  which  takes  more  or  less  nearly  the  form  of 
the  piece  of  copper  used.)  In  this  experiment  how  many  sub- 
stances entered  into  action  and  how  many  new  ones  were  formed  ? 


DECOMPOSITION   AND    COMBINATION  17 

Experiment  19.* 

Materials : 
Lumps  of  charcoal,  thoroughly  dried  by  heating. 

Apparatus: 

Oxygen  generator,  or  cylinder  of  compressed  oxygen  provided 
with  a  soda-lime  tube  or  with  a  wash  bottle  containing  a 
30  per  cent  solution  of  potassium  hydroxide. 
Small  combustion  furnace  (with  4-10  burners). 
Hard-glass  tubing. 
Glass  and  rubber  tubing  for  connections. 

Place  a  few  lumps  of  dried  charcoal  in  a  hard-glass  tube  in  a 
small  combustion  furnace.  Provide  the  tubes  with  corks  and 
connect  one  end  with  the  oxygen  gener- 
ator, the  other  with  a  delivery  tube. 
Pass  oxygen  through  the  apparatus  to 
expel  the  air.  Immerse  the  end  of  the 
delivery  tube  in  limewater  and  continue 
to  pass  pure  oxygen  through  the  appara- 
tus. Is  the  limewater  affected  by  the 
pure  oxygen? 

Heat  the  hard-glass  tube  gently  at 
first,  then  gradually  raise  the  heat  to 
redness.  Pass  a  very  slow  current  of 
oxygen  over  the  heated  carbon  into  the 
limewater.  What  occurs?  What  gas 
has  been  formed? 

If  the  experiment  is  continued  long 
enough,  the  charcoal  will  disappear,  pIG>  2o.  — Oxygen  generator 
leaving  only  a  small  quantity  of  white  using  fused  sodium  peroxide 
or  gray  ash.  Except  for  this  ash,  and  waier-  Oxygen  pre- 
charcoal  consists  entirely  of  a  substance  ±^^.°^ 
called  carbon.  This  substance,  when  this  style  of  generator  is 
raised  to  a  sufficiently  high  temperature,  employed  limewater  may 
combines  with  oxygen.  What  sub-  be  used  in  both  the  wash 
stance  is  the  product  of  this  combina-  ^£  ^om£j± 
tion?  tirely. 

Air  contains  oxygen,  and  exactly  the 

same  chemical  action  takes  place  when  charcoal  burns  in  a  draft  of 
air  as  when  it  burns  in  pure  oxygen.  Is  any  heat  produced  in 
this  combination?  What  practical  use  is  made  of  this  chemical 
change  ? 


CHAPTER  III 
ELEMENTS 

WATER,  which  is  one  of  the  decomposition  products  of 
sugar  (see  Expt.  15),  may,  as  we  have  seen  in  Experiment  16, 
be  itself  decomposed  into  hydrogen  and  oxygen.  In  Experi- 
ment 14  one  of  the  products  obtained  in  the  decomposition 
of  potassium  chlorate  is  potassium  chloride,  a  white  solid. 
If  this  substance  is  highly  heated,  it  melts,  and  if  an  electric 
current  is  passed  through  the  molten  mass,  decomposition 
occurs,  the  products  being  a  soft  metal,  called  potassium, 
and  a  greenish  yellow  gas,  called  chlorine. 

While,  therefore,  water  is  a  simpler  substance  than  sugar, 
it  is  less  simple  than  hydrogen  and  oxygen ;  and  while 
potassium  chloride  is  a  simpler  substance  than  potassium 
chlorate,  it  is  evidently  less  simple  than  potassium  and 
chlorine. 

When  limestone  is  heated  in  a  limekiln,  quicklime  and 
carbon  dioxide  (carbonic  acid  gas)  are  produced.  (See  Expt. 
17.)  But  carbon  dioxide,  as  we  have  seen  (Expt.  19),  is 
composed  of  the  simpler  substances,  carbon  and  oxygen. 
Similarly,  quicklime  is  a  compound  of  a  metal  called  calcium 
and  the  gas  oxygen. 

We  see,  then,  that  the  products  of  some  decompositions 
can  in  their  turn  undergo  decomposition.  However,  there 
are  a  number  of  substances  which  it  has  not  been  found 
possible  to  decompose.  Among  these  are  hydrogen,  oxygen, 
potassium,  chlorine,  calcium,  mercury,  and  carbon. 

Substances  which  we  cannot  decompose  are  known  as  elements. 
This  is  the  only  sense  in  which  the  word  element  is  used  in 
chemistry.  When  we  speak,  as  we  commonly  do,  of  wind 

18 


THE  HON.  ROBERT  BOYLE.  — 1626-1691. 

The  great  English  chemist  who  originated  the  modern  conception  of 
elements.  Born  in  Ireland,  a  son  of  the  first  Earl  of  Cork,  Boyle  was 
educated  in  England  and  spent  most  of  his  life  at  Stalbrige,  Dorsetshire. 
He  was  a  member  of  the  "  Invisible  College,"  an  association  of  men  de- 
voted to  the  new  experimental  philosophy,  and  of  the  Royal  Society,  into 
which  the  Invisible  College  developed  (1663).  Boyle's  predecessors  had 
studied  chemistry  with  a  view  to  its  applications  to  medicine  or  to  the 
transformation  of  the  baser  metals  into  gold.  He  studied  it  with  the 
single  purpose  of  discovering  the  truth. 


ELEMENTS  19 

and  rain  as  "  the  elements,"  or,  as  the  ancients  did,  of  fire, 
air,  water,  and  earth  as  the  elements,  we  are  not  speaking 
scientifically,  but  rather  poetically.  It  is  not  even  permis- 
sible to  speak  of  quicklime  and  carbon  dioxide  as  elements 
of  limestone,  though  we  may  call  them  the  constituents  of 
limestone.  The  elements  of  limestone  are  calcium,  carbon, 
and  oxygen.  In  science  every  word  has  a  very  definite 
meaning,  and  words  of  slightly  different  signification  may 
not  be  interchanged,  as  they  frequently  are  in  common 
speech. 

Recent  investigation  growing  out  of  the  discovery  of  radio- 
activity has  shown  that  some  of  the  elements,  such  as  uranium, 
thorium,  and  radium,  gradually  change  into  other  elements.  No 
means  has  yet  been  found  to  cause,  or  prevent,  or  in  any  way  to 
control,  such  changes,  which  are  nevertheless  going  on  at  an  entirely 
definite  rate.  The  distinction  between  this  kind  of  change  and 
decomposition  proper  can  scarcely  be  made  clear  without  reference 
to  the  atomic  theory,  which  will  be  outlined  later.  (See  Chapter 
VI.) 

At  present  (1913)  eighty- three  substances  are  officially 
recognized  as  elements  by  an  international  committee  of  the 
leading  chemical  societies  of  the  world.  Some  of  these  are 
familiar  substances  like  iron,  gold,  silver,  copper,  carbon 
(charcoal),  and  sulphur;  others  are  substances  rarely  heard 
of  in  ordinary  speech.  A  list  of  these  eighty-three  sub- 
stances will  be  found  at  the  end  of  Chapter  VI.  In  addition 
to  these  there  are  a  few  other  rare  substances  which  in  all 
probability  are  also  elements,  but  which  have  not  been 
investigated  thoroughly  enough  to  secure  official  recognition. 

Eleven  of  the  recognized  elements  are  gases.  Of  these  the  most 
important  are  oxygen,  hydrogen,  nitrogen,  and  chlorine.  Two 
elements  are  liquids,  one  of  which,  mercury,  is  familiar  from  its 
use  in  thermometers  and  barometers,  while  the  other,  bromine, 
is  a  disagreeable-smelling,  red,  fuming  substance.  Of  the  seventy 
solid  elements  several  examples  are  given  in  the  preceding  para- 
graph. 


20  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Gas,  liquid,  and  solid  are  the  three  physical  states  of  matter 
(a  general  term  for  all  substances).  The  elements  which 
under  ordinary  conditions  are  gases  can  be  changed  into 
liquids  and  solids  by  more  or  less  intense  cooling  and  com- 
pression. Many  of  those  which  under  ordinary  conditions 
are  solids  can  easily  be  melted  by  heating,  e.g.  tin,  lead, 
sulphur.  They  thus  become  liquids.  By  further  heating 
many  of  them  have  been  converted  into  gases,  e.g.  sodium, 
sulphur,  mercury,  bromine.  There  can  be  little  doubt, 
then,  that  under  suitable  conditions  every  element  can  be 
made  to  exist  in  all  three  physical  states,  and  when  we  speak 
of  oxygen  as  a  gas  or  of  sulphur  as  a  solid,  it  is  understood 
that  we  are  referring  to  the  ordinary  temperature  of  a  room, 
about  20°  C.  (68°  F.). 

Metals  and  Non-Metals 

The  great  majority  of  the  solid  elements,  and  one  of  the 
two  liquids  (mercury),  are  classed  as  metals.  Metals 
have  certain  chemical,  and  the  following  physical, 
characteristics:  (i)  A  bright  luster,  when  polished;  (2)  good 
conducting  power  for  heat;  (3)  good  conducting  power  for 
electricity.  Among  the  elements  of  this  class  are  the  familiar 
metals,  iron,  tin,  zinc,  copper,  silver,  gold,  etc.,  and  other 
important  but  less  familiar  substances,  such  as  sodium, 
potassium,  calcium,  and  radium.  Among  the  non-metals 
are  such  solids  as  carbon  (which  exists  in  the  three  forms  of 
charcoal,  graphite,  and  diamond),  sulphur,  phosphorus,  and 
iodine;  the  evil-smelling  red  liquid,  bromine;  and  all  the 
gaseous  elements. 

Experiment  20. 

Examine  samples  of  the  following  elements  and  classify  them 
as  metals  and  non-metals:  iron,  platinum,  sulphur,  phosphorus, 
gold,  silver,  copper,  carbon  (charcoal),  iodine,  zinc,  calcium, 
magnesium,  sodium,  potassium,  mercury,  bromine. 


ELEMENTS  21 

Experiment  21. 

Materials  : 

Covered  jars  of  chlorine,  oxygen,  hydrogen,  and  nitrogen. 

Examine  specimens  of  the  four  common  gaseous  elements. 
Remove  the  cover  of  each  jar  slightly,  and  waft  a  very  little  of  the 
gas  towards  the  nose.  Be  especially  careful  not  to  take  a  full  breath 
of  the  chlorine.  Which  of  these  four  gases  is  readily  distinguished 
by  its  color  and  odor?  Note  the  different  effects  of  the  other 
three  upon  a  burning  splint  of  wood. 


CHAPTER  IV 
COMPOUNDS 

THE  products  of  chemical  combination  of  the  elements 
are  called  compounds.  Thus,  water  is  a  compound  of  oxygen 
and  hydrogen;  salt  is  a  compound  of  sodium  (a  metal)  and 
chlorine  (a  yellow  gas) ;  saltpeter  is  a  compound  of  the  metal 
potassium  with  the  gaseous  elements  nitrogen  and  oxygen; 
and  sugar  is  a  compound  of  carbon  with  hydrogen  and  oxygen. 

A  compound  is  to  be  clearly  distinguished  from  a  mixture. 
Sulphur  and  iron  can  be  mixed  by  grinding  the  two  together 
in  a  mortar.  In  the  mixture  each  of  the  two  elements 
retains  its  individual  characteristics.  The  iron  is  still 
attracted  by  a  magnet.  Carbon  disulphide  dissolves  out 
the  sulphur,  leaving  the  iron  undissolved;  hydrochloric 
acid  dissolves  the  iron,  leaving  the  sulphur  untouched.  But 
when  iron  alid  sulphur  are  heated  together,  a  new  substance, 
iron  sulphide,  is  formed,  which  is  entirely  different  from 
either  of  its  elements.  It  is  not  attracted  by  the  magnet; 
carbon  disulphide  dissolves  out  nothing  from  it,  while  it 
dissolves  completely  in  hydrochloric  acid,  liberating  a  gas 
different  from  that  produced  by  the  action  of  the  acid  on 
iron. 

Experiment  22.* 

Materials  : 

Iron  powder  or  fine  filings. 

Sulphur. 

Carbon  disulphide. 

Iron  sulphide. 
Apparatus : 

Mortar  and  pestle. 

Magnet. 

22 


COMPOUNDS 


23 


to  bend  it.  To  produce  a  long,  narrow, 
yellow  flame,  provide  the  Bunsen 
burner  with  a  "  wing  top,"  and  close 
the  air  holes  at  the  base  of  the  burner. 
Hold  the  glass  above  the  dark  inner 
cone  of  the  flame  (which  is  cool) 
and  keep  it  rotating  until  soft  enough 
to  bend. 


Grind  together  in  a  mortar  about  2  grams  each  of  sulphur  and 
iron.     Divide  the  mixture  into  two  portions.     Place  one  portion 
in  a  test  tube  and  heat  to  redness.     Do  you  observe  any  evidence 
of  chemical  action?     Allow  the 
test  tube  to  cool,  break  it,  and 
examine   the  contents.     Grind 
these   and    compare   with   the 
unheated   portion.     Make   the 
following   tests    upon    each    of 

these  two  powders,  comparing  FIG-  2I-  —  Sojten ing  glass  tubing  in  order 
the  results : 

(a)  Pass   a   magnet   through 
the  powder.     If  both  powders 
are    attracted  by  the  magnet, 
shake     the     magnet     and     see 
whether  there  is  in  either  case 
any  evidence  of  a  separation  of 

the  iron  and  sulphur  from  each  other ;  also  which  powder  is  more 
strongly  attracted. 

(b)  Shake  a  little  of  the  powder  in  a  test  tube  with  carbon 
disulphide.     Pour  off  the  carbon  disulphide  through  a  filter  on 
to  a  watch  glass  and  set  aside  in  a  warm  place  but  not  near  a  flame. 

When  the  carbon  disulphide  has 
evaporated,  is  a  residue  left  in  either 
watch  glass?  What  is  this  residue? 
(c)  Treat  a  portion  of  the  powder 
in  a  test  tube  with  dilute  hydro- 
chloric acid.  Note  the  odors.  Also 
treat  a  portion  of  the  iron  powder 
with  dilute  hydrochloric  acid.  In 
this  test,  which  powder  gives  an  odor 
identical  with  that  given  by  the  iron 
itself?  If  the  differences  between 


FIG.  22.  —  Bending  glass  tubing. 
Remove    the    softened    glass 


from  the  flame  and  immedi-    the  mixture  of  iron  and  suiphur  and 

ately  bend  it  to  the  desired      , 

angle  the  compound  prepared  in  this  ex- 

periment are  not  sufficiently  marked 

(as  may  happen  if  some  of  the  iron  and  sulphur  have  not  reacted 
together),  the  above  comparisons  may  also  be  made  between  the 
mixture  and  a  portion  of  the  sample  of  iron  sulphide  supplied. 

Refer  to  your  notes  on  Experiment  18  (p.  16)  and  describe  the 
compound  of  copper  and  sulphur,  noting  differences  between  that 
compound  and  its  elements. 


24  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Air  is  a  mixture  of  the  two  gases,  nitrogen  and  oxygen. 
A  similar  mixture  can  be  made  of  hydrogen  and  oxygen. 
This  latter  mixture  is,  of  course,  not  air,  but  it  is  a  clear, 
colorless  gas  looking  exactly  like  air,  and  also  like  the  unmixed 
elements  —  hydrogen  and  oxygen.  But  when  oxygen  and 
hydrogen  combine,  the  resulting  compound,  water,  is  a  liquid, 
entirely  unlike  the  elements  from  which  and  of  which  it 
is  formed.  The  compound  (water)  can  be  produced  by  set- 
ting fire  to  the  gaseous  mixture  of  oxygen  and  hydrogen. 

Further  Discussion  of  the  Subject  Matter  of  Chemistry 

Having  learned  that  all  substances  can  be  resolved  into 
a  limited  number  of  elements,  we  are  prepared  to  add  some- 
thing to  the  definition  of  the  subject  matter  of  chemistry 
made  in  Chapter  I.  In  studying  chemistry  we  examine 
bodies  or  objects  with  special  reference  to  their  composition. 
We  endeavor  to  find  out  what  substances  the  objects  under 
consideration  are  made  of,  what  elements  they  contain,  and 
whether  these  elements  are  present  in  the  free  state  or  com- 
bined into  compounds.  Chemical  analysis  is  the  art  of 
finding  out  the  composition  of  bodies.  Chemistry  is  the 
science  which  treats  of  the  composition  of  bodies.  This 
is,  of  course,  not  intended  as  a  complete  definition  of  chem- 
istry, for  the  science  investigates  not  only  what  substances 
are  present  in  a  given  body,  but  also  under  what  conditions 
these  substances  are  transformed  into  other  substances  by 
rearrangement  of  the  elements. 

Nomenclature  of  Compounds 

The  number  of  chemical  compounds  of  the  eighty-odd 
elements  is  enormous.  To  provide  systematic  names  for 
them  all  many  devices  are  required,  but  only  two  of  the 
fundamental  principles  of  nomenclature  require  consideration 
at  this  point. 


COMPOUNDS  25 

1.  The  suffix  -ide  implies  that  no  elements  are  present, 
other  than  those  mentioned  in  the  name  of  the  compound. 
Thus,  sodium  chloride  (common  salt)  contains  no  elements 
but  sodium  and  chlorine;   ferrous  sulphide,  none  but  iron 
and  sulphur;    calcium  oxide,  none  but  calcium  and  oxygen, 
etc. 

2.  The   suffix    -ate    (also    the    less   common   one    -lie) 
implies  that,  in  addition  to  the  elements  named,  the  com- 
pound contains  oxygen.     Thus,  potassium  nitrate  (saltpeter) 
contains  potassium,  nitrogen,  and  oxygen;   potassium  chlorate 
is  a  compound  of  potassium,   chlorine,   and   oxygen;    and 
magnesium  sulphate  (Epsom  salt)  is  composed  of  magnesium, 
sulphur,  and  oxygen. 

EXERCISE 

What  elements  do  the  following  compounds  contain :  (i)  Calcium 
oxide,  (2)  Magnesium  nitrate,  (3)  Silver  chloride,  (4)  Hydrogen 
sulphide,  (5)  Sodium  sulphate,  (6)  Gold  chloride,  (7)  Potassium 
iodide,  (8)  Magnesium  iodate,  (9)  Sodium  sulphite,  (10)  Calcium 
phosphate  ? 


CHAPTER  V 
CHEMICAL   NOTATION 

CHEMISTS  represent  each  element  by  a  symbol,  usually 
the  initial  letter  of  the  Latin  name,  which  in  most  cases  is 
identical  with  the  initial  letter  of  the  English  name.  Ex- 
amples : 

Oxygen,  O  Nitrogen,  N 

Hydrogen,  H  Carbon,  C 

Iron  (Ferrum),  Fe  Potassium  (Kalium),  K 

Tin  (Stannum),  Sn 

Where  the  names  of  two  or  more  elements  have  the  same 
initial  the  symbols  of  all  but  one  have  a  second  characteristic 
letter  added  to  the  initial.  Thus : 

Boron,  B  Sulphur,  S 

Barium,  Ba  Silicon,  Si 

Bromine,  Br  Strontium,  Sr 

Carbon,  C  Silver  (Argentum),  Ag 

Chlorine,  Cl  Sodium  (Natrium);  Na 

Cobalt/Co 
Chromium,  Cr 
Copper  (Cuprum),  Cu 

Compounds  are  represented  by  formulas  made  up  of  the 
symbols  of  the  composing  elements.  Thus:  Ferrous  sul- 
phide, FeS ;  Calcium  oxide,  CaO.  To  the  chemist  the 
formula  signifies  not  merely  the  qualitative  but  also  the 
quantitative  composition  of  the  compound  —  not  only  what 
elements  it  contains,  but  in  what  proportions  they  are  present. 
For  this  purpose  the  formulas  of  most  compounds  contain 
some  figures  in  addition  to  the  symbols  of  their  elements. 
Thus:  Water,  H2O;  Sulphuric  acid,  H2SO4;  Potassium 

26 


BARON  JONS  JAKOB  BERZELIUS. — 1779-1848. 

The  Swedish  chemist  who  originated  our  modern  system  of  chemical  nota- 
tion. Berzelius,  the  most  influential  chemist  of  the  early  part  of  the  nineteenth 
century,  excelled  as  an  experimenter,  as  a  philosopher,  and  as  a  teacher.  He 
discovered  several  of  the  elements  and  determined  the  atomic  (or  "  combining  ") 
weights  of  those  previously  known. 


CHEMICAL    NOTATION  27 

chlorate,  KC1O3;    Carbon  monoxide,  CO,  but  Carbon  diox- 
ide, CO2 ;  Cane  sugar,  Ci2H22On ;  etc. 

Chemical  changes  or  reactions,  as  they  are  often  called, 
are  represented  by  equations,  one  side  of  which  is  made  up 
of  the  formulas  of  the  reacting  substances  (together  with 
certain  figures),  the  other  side  of  the  formulas  of  the  products 
of  the  reaction.  Thus : 

2  H2  +  O2  =  2  H2O,     or    2  H2  +  O2  ->  2  H2O 
signifies  that  hydrogen  and  oxygen  unite,  forming   water; 

2  KC1O3  =  2  KC1  +  3  O2 

that  potassium  chlorate  decomposes  into  potassium  chloride 
and  oxygen; 

Fe  +  S  =  FeS 

that  iron  and  sulphur  combine  to  form  ferrous  sulphide;  and 

AgN03  +  NaCl  =  AgCl  +  NaNO3 

that  silver  nitrate  and  sodium  chloride  (common  salt)  react, 
forming  silver  chloride  and  sodium  nitrate. 

The  table  on  p.  33  gives  the  names  and  symbols  of  all 
the  eighty-three  substances  accepted  as  elements  in  the 
year  1913  by  the  International  Committee  of  Chemists 
referred  to  above  (p.  19). 

The  twenty-six  elements  of  chief  interest  to  the  house- 
keeper are  given  also  in  the  table  on  inside  of  back  cover. 

EXERCISE 

Referring  to  the  table  at  the  end  of  Chapter  VI  for  the 
interpretation  of  the  symbols,  write  names  for  the  compounds 
represented  by  the  following  formulas-. 

(i)  FeS,  (2)  K2S,  (3)  Na2C03,  (4)  KNO3,  (5)  Ca(NO3)2,  (6)CaS04, 
(7)  MgCl2,  (8)  FeP04,  (9)  KC103,  (10)  HgO. 

Write  formulas,  omitting  figures,  for  the  compounds 
whose  names  follow : 

(i)  Silver  iodide,  (2)  Sodium  nitrate,  (3)  Potassium  iodate, 
(4)  Magnesium  nitride,  (5)  Calcium  sulphate. 


CHAPTER  VI 
THE   ATOMIC   THEORY 

OTJR  chemical  formulas  are  an  outgrowth  of  the  atomic 
theory,  originated  by  John  Dalton,  an  English  teacher 
and  chemist,  about  1803.  According  to  Dal  ton's  theory 
all  substances  are  made  up  of  minute  particles,  which  (in 
the  modern  terminology  of  the  theory)  are  called  molecules 
(diminutive  from  Latin,  moles,  mass).  The  smallest  visible 
particle  of  any  substance  contains  millions  of  such  mole- 
cules. 

Lord  Kelvin  estimated  that  if  a  drop  of  water  were  magnified 
to  the  size  of  the  earth,  the  molecules  would  appear  larger  than 
small  shot  but  smaller  than  cricket  balls.  Even  invisible  gases 
are  regarded  as  composed  of  molecules,  and  it  has  been  estimated 
that  one  cubic  centimeter  of  gas  (measured  at  ordinary  tempera- 
ture and  pressure)  contains  approximately  thirty  million  million 
million  molecules. 

The  molecules  of  each  pure  substance  (whether  element  or 
compound)  are  conceived  of  as  being  exactly  like  one  another 
but  different  from  those  of  every  other  substance.  The 
difference  recognized  is  a  difference  of  mass,  and  weighing  is 
our  most  familiar  way  of  comparing  masses.  All  the  mole- 
cules of  any  given  substance,  such  as  water,  are  equal  in 
weight,  but  the  weight  of  a  water  molecule  is  different  from 
that  of  an  alcohol  molecule. 

The  molecules  of  a  substance  cannot  be  in  any  way  sub- 
divided without  destroying  the  substance  —  not  annihilating 
it,  but  converting  it  into  other  substances.  In  chemical 
decompositions  the  molecules  of  the  original  substance  are 
split  up  into  the  smaller  molecules  of  the  decomposition 

28 


JOHN  D ALTON.  — 1766-1844. 

Dalton  originated  the  modern  atomic  theory  and  roughly  determined 
the  atomic  weights  of  several  elements. 


THE    ATOMIC    THEORY  29 

products.  Thus,  when  calcium  carbonate  (limestone  or  chalk) 
decomposes  into  calcium  oxide  (quicklime)  and  carbon 
dioxide  (see  Expt.  17,  p.  13),  we  conceive  that  each  mole- 
cule of  the  calcium  carbonate  has  split  up  into  two  smaller 
molecules  —  one  the  molecule  of  calcium  oxide,  the  other 
the  molecule  of  carbon  dioxide. 

The  molecules  of  compounds  are  conceived  to  be  made 
up  of  particles  of  the  constituent  elements  of  the  compounds. 
Such  particles  of  the  elements  are  known  as  atoms.  Thus, 
the  molecule  of  calcium  oxide  would  contain  at  least  one  atom 
of  calcium  and  one  atom  of  oxygen. 

The  symbols  of  the  elements  are  used  to  represent  the 
atoms.  The  formula,  CaO,  stands  for  a  molecule  of  calcium 
oxide,  composed  of  one  atom  of  the  element  calcium  and  one 
atom  of  the  element  oxygen.  Similarly,  the  formula,  KC1, 
stands  for  a  molecule  of  the  compound  potassium  chloride, 
consisting  of  one  atom  of  the  element  potassium  (K)  and  one 
atom  of  the  element  chlorine  (Cl). 

The  formula,  CO2,  represents  a  molecule  of  carbon  dioxide, 
consisting  of  one  atom  of  carbon  united  to  two  atoms  of 
oxygen ;  the  formula,  H2O,  a  molecule  of  water,  composed  of 
two  atoms  of  hydrogen  united  to  one  atom  of  oxygen ;  and 
the  formula,  KClOs,  a  molecule  of  potassium  chlorate  con- 
taining one  atom  each  of  .potassium  and  chlorine  and  three 
atoms  of  oxygen.  The  chemists'  reasons  for  regarding  a 
molecule  of  carbon  dioxide  as  containing  two  atoms  of  oxygen 
rather  than  one  need  not  concern  us  here  —  though  we  may 
note  that  there  is  another  compound  of  carbon  and  oxygen, 
called  carbon  monoxide,  whose  molecule  is  regarded  as  com- 
posed of  one  atom  of  each  of  the  two  elements.  This  sub- 
stance, carbon  monoxide,  is  represented  by  the  formula, 
CO. 

The  molecules  of  any  substance  —  for  instance  the  cal- 
cium carbonate  molecules  in  a  piece  of  limestone  —  are  con- 
ceived to  be  in  motion.  Physical  changes  may  often  be 


30  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

accounted  for  by  changes  in  the  arrangement  of  the  mole- 
cules with  respect  to  one  another  or  in  the  rate  or  manner  of 
motion  of  the  molecules.  Heating,  for  example,  is  believed 
to  make  the  molecules  move  faster.  But  any  change  which 
results  in  a  disruption  of  the  molecule  or  a  rearrangement  of 
the  atoms  so  as  to  form  new  molecules  is  a  chemical  change. 
In  calcium  carbonate  such  a  disruption  takes  place  when  the 
temperature  has  become  sufficiently  high.  According  to 
the  theory,  the  molecules  have  then  acquired  so  rapid  a 
motion  that  they  break  asunder  into  molecules  of  calcium 
oxide  and  molecules  of  carbon  dioxide. 

In  the  electrolysis  of  water  the  atoms  of  hydrogen  and 
oxygen  composing  the  molecule  of  water  separate  from  one 
another.  The  hydrogen  atoms  set  free  at  the  one  electrode 
unite  in  pairs  to  form  hydrogen  molecules,  H2 ;  and  the  oxygen 
atoms  set  free  at  the  other  electrode  likewise  unite  in  pairs, 
forming  oxygen  molecules,  O2.  Two  molecules  of  water 
thus  yield  two  molecules  of  hydrogen  and  one  molecule  of 
oxygen. 

This  is  represented  by  the  equation : 

2  H2O  =  2  H2  +  O2 

The  reasons  for  regarding  the  oxygen  (and  hydrogen)  mole- 
cules as  consisting  of  two  atoms  need  not  be  considered  here. 
Conversely,  when  hydrogen  burns  in  oxygen,  the  atomic 
theory  regards  the  atoms  of  hydrogen  and  oxygen  as  uniting, 
two  of  the  former  with  one  of  the  latter,  into  molecules  of 
water : 

2  H2  +  02  =  2  H2O 

Before  the  reaction  the  atoms  of  hydrogen  are  united  with 
each  other  in  pairs,  forming  hydrogen  molecules ;  and  the 
atoms  of  oxygen  are  united  in  pairs,  forming  oxygen  mole- 
cules. After  the  reaction  the  atoms  are  combined  in  groups 
of  three  —  two  hydrogen  and  one  oxygen  —  into  molecules 
of  water,  thus,  H — O — H.  We  commonly  abbreviate  the 
formula  H— O— H  into  H2O. 


THE    ATOMIC    THEORY  31 

In  such  reactions  as  that  of  silver  nitrate  with  sodium 
chloride  (Expt.  6,  p.  6)  there  is  an  exchange  of  partners 
among  the  atoms.  Thus,  the  silver  atoms  separate  from  the 
nitrogen  and  oxygen  atoms,  with  which  they  are  originally 
united,  and  combine  with  the  chlorine  atoms  of  the  sodium 
chloride,  forming  molecules  of  silver  chloride;  and  the 
sodium  atoms,  originally  united  with  the  chlorine  atoms, 
transfer  their  allegiance  from  chlorine  to  nitrogen  and  oxygen. 

AgNO3  +  NaCl  =  AgCl  +  NaNO3 

By  measuring  the  proportions  in  which  the  elements  com- 
bine with  one  another  and  reasoning  from  the  results,  chem- 
ists have  arrived  at  definite  conclusions  regarding  the  rela- 
tive weights  of  the  various  kinds  of  atoms.  Hydrogen,  it  is 
concluded,  has  the  lightest  atom.  The  oxygen  atom  is  about 
sixteen  (more  accurately  15.87)  times  as  heavy  as  the  hydro- 
gen atom.  The  carbon  atom  is  three-fourths  as  heavy  as  the 
oxygen  atom  or  about  twelve  times  as  heavy  as  the  hydro- 
gen atom.  The  heaviest  atom  known  is  that  of  uranium, 
which  weighs  about  237  times  as  much  as  the  hydrogen 
atom. 

The  relative  weights  of  the  atoms  are  given  in  the  table  on 
p.  33.  A  table  of  atomic  weights  might  be  made  in  which 
the  weight  of  a  hydrogen  atom  was  taken  as  the  unit.  In 
such  a  table  the  atomic  weight  of  oxygen  would  be  15.87, 
meaning  that  one  atom  of  oxygen  weighs  15.87  times  as 
much  as  one  atom  of  hydrogen,  and  the  atomic  weight  of 
carbon  would  be  11.9,  meaning  that  a  carbon  atom  weighs 
11.9  times  as  much  as  a  hydrogen  atom.  This  was  actually 
the  basis  upon  which  the  first  tables  of  atomic  weights  were 
made  out.  But  the  present  international  committee  pre- 
fers to  take  the  atomic  weight  of  oxygen  as  exactly  16  and 
that  of  hydrogen  as  1.008  (16  +  15.87  =  1.008).  The  ratio 
between  any  two  atomic  weights  is  the  same  on  the  one  basis 
as  on  the  other,  and  it  is  only  the  ratios  which  chemists  profess 


32  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

to  know,  the  atoms  themselves  being  immeasurably  small, 
and  therefore  of  unknown  absolute  weight. 

As  already  stated,  the  atomic  theory  in  its  modern  form  dates 
from  the  beginning  of  the  nineteenth  century.  However,  the 
view  that  matter  is  not  infinitely  divisible  but  is  made  up  of  minute 
indivisible  particles  (atoms)  had  been  held  by  many  philosophers 
of  ancient  times  and  by  some  of  the  great  modern  scientists  who 
lived  before  Dalton's  day,  for  instance,  by  Robert  Boyle  (1626- 
1691)  and  by  Sir  Isaac  Newton  (1642-1727).  But  the  idea  that 
each  element  has  an  atom  of  a  definite  weight,  and  that  the  smallest 
particles  (molecules)  of  every  compound  are  made  up  of  atoms 
of  the  elements  of  that  compound,  originated  with  Dalton. 

The  word  atom  (Greek,  atomos,  from  a,  not,  and  temno,  cut) 
implies  indivisibility.  Until  recently  the  atoms  of  the  chemical 
elements  were  regarded  as  absolutely  indivisible.  The  investi- 
gations arising  out  of  the  discovery  of  radioactivity  have  shown 
that  some  of  the  elements  (especially  some  of  those  having  very 
heavy  atoms)  are  gradually  undergoing  a  spontaneous  trans- 
mutation into  other  elements  of  lower  atomic  weight.  In  under- 
going such  transmutation  these  elements  emit  certain  radiations, 
some  of  which  are  believed  to  consist  of  particles  much  smaller 
than  atoms.  These  particles  are  called  electrons.  Accordingly, 
it  appears  not  improbable  that  the  atomic  theory  will  receive  an 
extension,  according  to  which  the  various  kinds  of  atoms  will 
be  regarded  as  aggregations  of  various  numbers  of  electrons. 

Up  to  the  present  no  means  have  been  found  of  controlling  the 
transmutations  of  the  radioactive  elements.  Accordingly,  while 
it  is  no  longer  permissible  to  define  an  element  as  a  substance 
which  cannot  be  decomposed,  it  is  still  permissible  for  us  to  apply 
the  term  element  to  those  substances  which  we  cannot  decompose, 
and  the  term  atom  to  the  theoretical  particle  which  remains 
intact  in  all  chemical  changes  that  are  not  accompanied  by  radio- 
activity. 


THE    ATOMIC    THEORY 


33 


INTERNATIONAL  ATOMIC  WEIGHTS,   1913 


Element 

Symbol 

Atomic 
Weight 

Element                         Symbol 

Atomic 
Weight 

Aluminium  .     . 

Al 

27.1 

Neodymium      .     . 

Nd 

144-3 

Antimony     .     . 

.     Sb 

1  20.  2 

Neon        .... 

Ne 

2O.2 

Argon       .     .     . 

.    A 

39-88 

Nickel      .... 

Ni 

58.68 

Arsenic    .     .     . 

.     As 

74.96 

Niton  (radium  ema- 

Barium   .     .     . 

.     Ba 

137-37 

nation)  .... 

Nt 

222.4 

Bismuth  .    .     . 

.     Bi 

208.0 

Nitrogen  .... 

N 

I4.OI 

Boron       .     .     . 

.     B 

II.O 

Osmium    .... 

Os 

190.9 

Bromine  .     .     . 

.     Br 

79.92 

Oxygen    .... 

0 

16.00 

Cadmium     .     . 

.     Cd 

112.40 

Palladium     .     .     . 

Pd 

106.07 

Caesium   .     .     . 

.     Cs 

132.81 

Phosphorus  .     .     . 

P 

31.04 

Calcium  .     .     . 

.     Ca 

40.07 

Platinum      .     .     . 

Pt 

195.2 

Carbon    .     .     . 

.     C 

12.00 

Potassium    .     .     . 

K 

39.10 

Cerium     .     .     . 

.     Ce 

140.25 

Praseodymium 

Pr 

140.6 

Chlorine  .    .     . 

.     Cl 

35.46 

Radium   .... 

Ra 

226.4 

Chromium    .     . 

.     Cr 

52.0 

Rhodium      .     .     . 

Rh 

102.9 

Cobalt     .     .     . 

.     Co 

58.97 

Rubidium     .     .     . 

Rb 

85.45 

Columbium  .     . 

.     Cb 

93-5 

Ruthenium  .     .     . 

Ru 

101.7 

Copper     .     .     . 

.     Cu 

63-57 

Samarium     .     .     . 

Sa 

150.4 

Dysprosium 
Erbium    .     .     . 

.     Dy 
.     Er 

162.5 
167.7 

Scandium     .     .     . 
Selenium       .     .     . 

Sc 
Se 

44.1 
79-2 

Europium     .     . 

.     Eu 

152.0 

Silicon      .... 

Si 

28.3 

Fluorine 

.     F 

IQ.  O 

Silver 

Ag 

107.88 

Gadolinium  .     . 

.     Gd 

A  v 

157.3 

Sodium    .... 

o 

Na 

23.00 

Gallium   .     .     . 

.     Ga 

69.9 

Strontium     .     .     . 

Sr 

87.63 

Germanium 

.     Ge 

72.5 

Sulphur    .... 

S 

32.07 

Glucinum     .     . 

.     Gl 

9.1 

Tantalum     .     .     . 

Ta 

181.5 

Gold    .... 

.     Au 

197.2 

Tellurium     .     .     . 

Te 

127-5 

Helium    .     .     . 

.     He 

3-99 

Terbium  .... 

Tb 

159.2 

Holmium      .     . 

.     Ho 

163.5 

Thallium.    .     .     . 

Ti 

204.0 

Hydrogen     .     . 

.     H 

1.008 

Thorium  .... 

Th 

232.4 

Indium    .     .     . 

.     In 

114.8 

Thulium  .... 

Tm 

168.5 

Iodine      .     .     . 

.     I 

126.92 

Tin      

Sn 

119.0 

Iridium    .     .     . 

.     Ir 

I93-I 

Titanium      .     .     . 

Ti 

48.1 

Iron 

Fe 

crt  Rj. 

Tungsten 

W 

184.0 

Krypton  .     .     . 

.     Kr 

0  3*°*t 

82.92 

Uranium       .     .     . 

U 

238.5  • 

Lanthanum  .     . 

.     La 

139.0 

Vanadium    .     .     . 

V 

51.0 

Lead   .... 

Pb 

207.10 

Xenon 

Xe 

I  ^O  2 

Lithium  .     .     . 

.     Li 

6.94 

Ytterbium      (Neo- 

•"•O^"6 

Lutecium      .     . 

.     Lu 

174.0 

ytterbium)     .     . 

Yb 

I72.O 

Magnesium  .     . 

.     Mg 

24.32 

Yttrium  .... 

Yt 

89.0 

Manganese  .     . 

.     Mn 

54-93 

Zinc     

Zn 

65.37 

Mercury  .     .     . 

.     Hg 

200.  6 

Zirconium     .     .     . 

Zr 

9O.6 

Molybdenum    . 

.     Mo 

96.0 

CHAPTER  VII 
THE   LAW   OF   DEFINITE   PROPORTIONS 

IT  Dal  ton's  atomic  theory  be  correct,  every  compound 
must  contain  its  elements  in  certain  definite  proportions  by 
weight.  Thus  a  water  molecule,  made  up  of  two  atoms  of 
hydrogen,  weighing  2  (or  more  precisely  2.016),  and  one 
atom  of  oxygen  weighing  16,  has  evidently  8  times  as  much 
of  oxygen  by  weight  as  of  hydrogen.  And  since  a  cupful 
(or  a  barrelful)  of  water  is  made  up  of  individual  molecules, 
every  one  of  which  contains  8  times  as  much  oxygen  as 
hydrogen,  the  cupful  (or  barrelful)  of  water  if  decomposed 
would  yield  8  times  the  weight  of  oxygen  as  of  hydrogen. 
Experiment  shows  that  this  is  true  no  matter  what  the 
quantity  of  water  used.  The  same  principle  applies  to 
every  compound. 

A  chemical  compound  always  contains  the  same  elements  in 
the  same  proportions  by  weight.  This  is  known  as  the  Law  of 
Definite  Proportions. 

This  principle  of  Definite  Proportions  is  not  confined  to 
reactions  of  combination.  It  governs  chemical  reactions 
of  all  kinds. 

The  molecule  of  calcium  carbonate,  CaCOs,  being  made 
up  of  one  atom  of  calcium,  weighing  40,  one  atom  of  carbon, 
weighing  12,  and  three  atoms  of  oxygen,  each  weighing  16, 
has  a  total  weight  of  40  +  12  +  48  =  100.  Similarly,  the 
molecular  weight  of  calcium  oxide,  CaO,  is  56  (40  +  16)  and 
that  of  carbon  dioxide,  COz,  is  44  (12  +  twice  16).  Accord- 
ing, then,  to  the  equation 

CaCO3  =  CaO  +  CO2 

100  parts  of  calcium  carbonate  decompose  into  56  parts  of 
calcium  oxide  and  44  parts  of  carbon  dioxide.     And  this  is 

34 


58-5 

143-5 

85 

Na  = 

35-5 

Ag  = 

108 

Na  = 

23 

Cl  = 

23.0 

Cl  = 

35-5 

N  = 

14 

30  = 

48 

58.5 

I43-5 

85 

THE    LAW    OF    DEFINITE    PROPORTIONS  35 

true,  whatever  the  units  in  which  we  express  the  weight. 
Thus  100  grains  of  calcium  carbonate  give  56  grains  of  cal- 
cium oxide  and  44  grains  of  carbon  dioxide ;  100  ounces  of 
calcium  carbonate  give  56  ounces  of  calcium  oxide  and  44 
ounces  of  carbon  dioxide ;  and  so  on  for  pounds,  tons,  grams, 
kilograms,  and  all  other  units  of  weight. 

So  also  170  parts  of  silver  nitrate  by  weight  react  with 
58.5  parts  of  salt  (sodium  chloride),  no  more  and  no  less: 

AgN03       +       NaCl       =         AgCl    +    NaNO3 

170 

Ag  =  108 

N  =  14 

30  =  16X3=^8 

170 

Every  pound  of  silver  nitrate  takes  58.5  -f-  170  =  0.344 
pound  of  salt,  and  every  ton  of  silver  nitrate  0.344  ton  of  salt. 
If  more  salt  is  used,  the  excess  will  be  left  unchanged.  If,  for 
instance,  one  pound  of  silver  nitrate  and  one  pound  of  salt  are 
brought  together  in  solution,  0.344  pound  of  the  salt  will  be 
used  up  in  precipitating  the  silver  nitrate  and  the  remaining 
0.656  pound  of  salt  will  be  left  in  the  water  unchanged. 

This  principle  is  of  some  importance  in  the  household 
applications  of  chemistry.  Baking  powders,  for  instance, 
should  be  so  made  as  to  contain  exactly  the  right  quantity 
of  soda  to  react  with  all  the  cream  of  tartar.  If  too  much 
of  either  constituent  is  used,  the  excess  will  remain  in  the 
cake  or  biscuit,  making  it  sour  or  bitter  as  the  case  may  be. 

EXERCISES 

i.  The  reaction  between  baking  soda  and  cream  of  tartar  is 
represented  by  the  equation : 

NaHC03  +      KHC4H4O6  =  KNaC4H406+  CO2  +  H2O 

Sodium  bicar-  Potassium  Potassium  Carbon 

bonate  or  bitartrate  or  sodium  tar-  dioxide 

baking  soda  cream  of  trate  or 

tartar  Rochelle  salt 


36  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Using  the  atomic  weights  of  the  table  on  the  inside  of  the  back 
cover  of  the  book,  calculate  how  many  pounds  of  pure  cream  of 
tartar  are  required  for  every  pound  of  baking  soda. 

2.  How  many  ounces  of  carbon  dioxide  are  obtainable  from  a 
pound  (16  ounces)  of  baking  soda  by  the  reaction  with  cream  of 
tartar  ? 

3.  100  pounds  of  cream  of  tartar  90  per  cent  pure  are  to  be 
made  up  into  baking  powder.     How  many  pounds  of  pure  baking 
soda  should  be  used? 

4.  When  baking  soda  is  heated,  washing  soda   (Na2COaX~-is 
formed  according  to  the  following  equation  : 

2  NaHCOa  =  Na2CO3  +  H2O  +  CO2 

This  equation  signifies  that  two  molecules  of  sodium  bicar- 
bonate are  converted  into  one  each  of  sodium  carbonate,  water, 
and  carbon  dioxide. 

How  many  pounds  of  washing  soda  would  100  pounds  of 
baking  soda  make  ? 

5.  100  grams  each  of  baking  soda  and  pure  cream  of  tartar  are 
mixed  and  used  as  a  baking  powder  in  making  a  batch  of  biscuits. 
How  much  baking  soda  will  be  left  over  when  the  cream  of  tartar 
has  all  been  acted  upon  ? 

6.  Assuming  that  the  baking  soda  left  over  in  Example  5  is  all 
converted  into  washing  soda  in  the  baking,  how  many  grams  of 
washing  soda  will  the  batch  of  biscuits  contain  ? 

Experiment  23. 

Materials : 

Potassium  bitartrate. 

Sodium  bicarbonate. 

Litmus  solution. 

25  cc.  graduated  cylinders. 

Dissolve  1.88  grams  potassium  bitartrate  in  50  cc.  of  hot  water 
in  a  beaker.  Keep  the  liquid  hot,  but  not  boiling,  and  stir  with 
a  glass  rod  until  all  the  solid  is  dissolved.  Dissolve  0.84  gram 
sodium  bicarbonate  in  20  cc.  of  cold  water.  Divide  each  solution 
into  two  exactly  equal  portions.  To  one  portion  of  each  add 
enough  litmus  solution  to  color  it  distinctly.  Observe  the  color 
the  litmus  takes  in  the  two  liquids.  Put  the  colored  bicarbonate 
solution  into  a  beaker  or  dish  and  gradually  pour  the  colored 
bitartrate  solution  (still  hot)  into  it.  What  do  you  observe? 
Hold  a  film  of  limewater  (calcium  hydroxide)  in  the  escaping  gas. 


THE    LAW    OF    DEFINITE    PROPORTIONS  37 

What  is  this  gas?  If  the  color  of  the  bicarbonate  solution  is  not 
changed,  add  some  of  the  second  portion  of  bitartrate  solution 
little  by  little,  until  the  color  does  change.  Then  add  the  un- 
colored  portion  of  bicarbonate  solution,  and  finally  the  remainder 
of  the  bitartrate  solution.  If  necessary,  dissolve  a  little  more 
bitartrate  and  add  it.  If  the  materials  are  perfectly  pure  (which 
they  often  are  not)  and  the  weighings  exact,  the  color  changes 
will  occur  when  the  half  portion  of  the  two  solutions  are  mixed 
and  again  when  the  whole  of  the  bitartrate  solution  has  been  added. 


CHAPTER  VIII 

COMPOUNDS    OF   THE    SAME   ELEMENTS    IN   DIF- 
FERENT  PROPORTIONS 

IF  different  numbers  of  atoms  of  two  elements  combine, 
the  molecules  formed  are  different.  Thus,  there  is  a  liquid 
substance,  similar  in  appearance  to  water,  which  yields  by 
decomposition  16  times  as  much  oxygen  by  weight  as  hydro- 
gen, i.e.  equal  volumes  of  the  two  gases.  This  substance  is 
known  as  hydrogen  peroxide.  A  mixture  of  3  parts  of  it 
with  97  parts  of  water  (a  3  per  cent  solution}  is  a  common 
article  of  commerce,  being  used  as  a  bleaching  agent  and  as 
an  antiseptic.  Now,  the  molecule  of  hydrogen  peroxide 
must  contain  16  times  as  much  oxygen  as  hydrogen;  that  is 
to  say,  one  atom  of  oxygen  to  every  atom  of  hydrogen.  It 
is  believed  to  contain  two  atoms  of  each  element  and  is  there- 
fore given  the  formula  H2O2. 

Similarly,  we  have  two  compounds  of  oxygen  and  carbon, 
both  gases,  (i)  carbon  monoxide,  CO,  and  (2)  carbon  dioxide, 
CO2;  two  oxides  of  copper,  viz.  (i)  cuprous  oxide,  Cu2O, 
a  red  solid,  and  (2)  cupric  oxide,  CuO,  a  black  solid ;  and  two 
chlorides  of  iron,  viz.  (i)  ferrous  chloride,  FeCl2,  a  greenish 
solid,  and  (2)  ferric  chloride,  FeCl3,  a  reddish  solid;  and 
there  are  many  other  instances  of  the  existence  of  more  than 
one  compound  of  the  same  elements.  Indeed,  there  are 
several  hundred  compounds  of  the  elements  carbon  and  hy- 
drogen (hydrocarbons)  and  thousands  of  compounds  of  the 
three  elements  carbon,  hydrogen,  and  oxygen. 

38 


COMPOUNDS    OF    THE    SAME    ELEMENTS  39 


Nomenclature  of  Such  Compounds 

Where  the  number  of  different  compounds  of  the  same 
elements  is  limited  to  two,  the  two  are  often  distinguished 
by  using  the  suffixes  -ous  and  -ic  on  the  adjective  part 
of  the  .name.  The  suffix  -ous  —  signifying  "  full  of  "  l  —  is 
applied  to  the  compound  containing  the  larger  proportion  of 
the  element  to  whose  name  the  suffix  is  attached.  Thus :  — 

Cuprous  oxide,  Cu2O ;  Cupric  oxide,  CuO. 

Ferrous  chloride,  FeCl2 ;  Ferric  chloride,  FeCl3. 

Sulphurous  acid,  .H^SOs ;   Sulphuric  acid,  H2S04. 

Mercurous  chloride,  HgCl ;  Mercuric  chloride,  HgCl2. 

Ferrous  sulphate,  FeSO4 ;   Ferric  sulphate,  Fe2(S04)3. 

Ferrous  chloride  has  one  atom  of  iron  to  every  two  atoms  of 
chlorine,  while  ferric  chloride  has  only  one  atom  to  every  three; 
sulphurous  acid  has  one  of  sulphur  to  every  three  of  oxygen,  while 
sulphuric  acid  has  only  one  to  every  four,  etc. 

EXERCISES 

Name  the  following  compounds  on  the  above  principle  : 

(i)  CuCl  and  CuCl2.  (2)  AuCl  and  AuCl3. 

(3)  HgN03  and  Hg(NO3)2.  (4)  SnCl2  and  SnCl4. 

(5)  HC1O2  and  HC103  (acids).        (6)  H3PO3  and  H3PO4  (acids). 

Another  means  of  distinguishing  compounds  of  the  same  elements 
in  different  proportions  is  to  modify  the  substantive  part  of  the 
name  with  a  prefix  indicating  the  number  of  atoms  of  the  element, 
whose  name  is  thus  modified,  contained  in  the  molecule  of  the 
compound.  The  prefixes  used  are  derived  from  the  Greek 
numerals  : 

Mono-  or  mon-,  one;  di-,  two;  tri-,  three;  tetra-  or  tetr-,  four; 
penta-  or  pent-,  five ;  hexa-  or  hex-,  six ;  hepta-  or  kept-,  seven ; 
octo-  or  oct-,  eight ;  etc. 

Carbon  monoxide,  CO ;  Carbon  dioxide,  C02. 

Nitrogen  trioxide,  N2O3 ;  Nitrogen  pentoxide,  N2Os. 

The  prefix  per-,  signifying  "  thorough,"  is  sometimes  used  to 
denote  that  the  compound  named  has  more  of  a  certain  element 

1  Compare  such  words  as  dangerous,  beauteous,  mysterious,  and  tyrannous. 


40  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

(usually  oxygen)  than  some  other  compound.  Thus :  hydrogen 
peroxide,  H2O2,  has  more  oxygen  than  water,  H2O ;  and  barium 
peroxide,  Ba02,  more  oxygen  than  barium  oxide,  BaO.  Also 
perchloric  acid,  HC1O4,  has  more  oxygen  than  chloric  acid, 
HC1O3,  and  perboric  acid,  HB03,  a  larger  proportion  of  oxygen 
(e.g.  to  one  atom  of  hydrogen)  than  boric  acid,  H3BO3. 

EXERCISES 

Name  the  following: 

(i)  PCla,  (2)  PC15,  (3)  P203,  (4)  P205,  (5)  S02,  (6)  S03,  (7)  PbO, 
(8)  PbO2. 


CHAPTER  IX 
COMBUSTION 

ONE  of  the  most  familiar,  as  well  as  one  of  the  most  use- 
ful, of  chemical  phenomena  is  combustion  or  burning.  Fire 
has  been  known  to  mankind  from  time  immemorial,  and 
advance  in  its  control  and  utilization  has  kept  pace  with 
the  progress  of  civilization.  Even  to-day,  when  electrical 
energy  is  so  much  made  use  of,  practically  our  only  source 
of  artificial  heat  is  combustion.  Our  rural  homes,  for  the 
most  part,  depend  upon  combustion,  not  merely  for  heat 
but  also  for  light,  and  even  the  electricity  which  lights  our 
towns  and  cities  comes  largely  from  power  generated  by 
the  burning  of  coal. 

Combustion  can  take  place  either  with  or  without  the 
phenomenon  of  flame.  Flame  appears  in  the  burning  of 
paper,  wood,  coal,  candles,  oils,  alcohol,  and  gas.  Charcoal 
and  coke,  however,  burn  without  flame.  As  charcoal  is 
made  by  heating  wood,  and  coke  by  heating  coal,  we  have 
flameless  combustion  in  the  later  stages  of  wood  and  coal 
fires. 

Experiment  24. 

Materials : 

Test  tube. 

Pieces  of  hard  wood. 

Cork  and  cork  borer,  or  one-holed  rubber  stopper. 

Glass  tube  drawn  to  a  tip  at  one  end. 

Provide  a  test  tube  with  a  tightly  fitting,  single-hole  cork  or 
rubber  stopper,  through  which  passes  a  short  piece  of  glass  tubing 
drawn  to  a  tip  at  the  upper  end.  Place  a  piece  of  dry,  hard  wood 
in  the  test  tube,  and  apply  heat.  Apply  a  match  to  the  smoke 
which  issues  from  the  glass  tip.  The  visible  part  of  the  smoke 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


consists  of  small  particles  of  solid  matter  and  minute  drops  of 

liquid.  But  these  solid  particles 
and  liquid  droplets  are  suspended 
in  invisible  gases,  which  are  them- 
selves combustible.  When  the 
gas  ceases  to  burn  and  will  not 
relight,  open  the  test  tube  and 
examine  the  residue  left  from  the 
wood.  What  is  it?  Heat  one 
end  of  it  in  the  Bunsen  flame  for 
a  minute  or  two.  On  withdraw- 
ing it  from  the  flame  note  whether 
it  is  burning,  and  if  so,  whether 
with  or  without  flame. 

In  the  light  of  this  experiment, 
how  do  you  account  for  the  fact 
that  a  wood  fire  shows  flame  in 
its  early  stages,  but  later  no  flame 
but  only  glowing  coals  ? 


Experiment  25. 

Materials : 

Hard-glass  test  tube. 
Soft  coal  in  small  pieces. 
Repeat   Experiment    24    in    a 
hard-glass   test  tube,  using  soft 
coal  instead  of  hard  wood.     The 
residue  left  in  the  test  tube  in  this  instance  is  coke. 


FIG.  23.  —  A  p  par  at  us  for  destructive 
distillation  of  wood  or  coal. 


Experiment  25  illustrates  the  process  of  manufacture 
of  the  illuminating  gas  known  as  "  coal  gas."  Before  the 
gas  is  delivered  into  the  mains  to  be  distributed  it  is  purified 
by  the  removal  of  the  solid  and  liquid  particles  which  con- 
stitute the  cloud.  In  the  purification  processes  some  of  the 
gaseous  products  also  are  eliminated  —  for  instance,  sul- 
phur compounds,  the  burning  of  which  would  yield  products 
injurious  to  health. 

Flame  occurs  only  in  the  combustion  of  gases.  Solid 
and  liquid  fuels  which  burn  with  flame  do  so  because  they  are 
converted,  wholly  or  partially,  into  gases  by  the  heat  pro- 


JOHN  MAYOW.  — 1645-1679. 

Mayow,  an  English  physician,  recognized  that  air  contained  a  constitu- 
ent concerned  m  combustion,  in  respiration,  and  in  the  rusting  of  metals, 
estimated  that  this  active  constituent  made  up  about  one  fourth  of  the 
1  found  that  it  was  present  in  saltpeter.     Mayow  called  the  active 
substance     fire-air     and  "  nitre-air."     We  call  it  oxygen 


COMBUSTION 


43 


duced  by  the  combustion.  The  reason  that  charcoal  and 
coke  burn  without  flame  is  that  (except  for  the  ash  which 
they  contain)  these  fuels  consist  wholly  of  the  element 
carbon,  which  is  not  converted  into  gas  by  the  heat  of  its 
own  combustion.  The  solid  carbon  combining  with  the  gas 
oxygen  yields  much  heat  —  so  much  that  it  is  heated  to 
incandescence  —  but  no  flame. 

We  have  next  to  consider  the  part  the  gases  of  the  air 
play  in  the  process  of  combustion. 

Experiment  26. 

Materials  : 

Supply  of  nitrogen  from  a  generator  or  gasometer. 

Supply  of  oxygen  from  a  generator  or  gasometer. 

Splint. 

Candle. 

Labels. 

Plunge  a  flaming  splint  into  (i)  a 
bottle  of  air,  (2)  a  bottle  of  oxygen, 
(3)  a  bottle  of  nitrogen.  Do  the 
same  with  a  lighted  candle. 

Experiment  27.* 

Apparatus : 

A  bell  glass  with   open  narrow 

neck.     Rubber  stopper  to  fit. 

A  basin   or  stoppered   sink,   or 

pneumatic  trough. 
A  porcelain  crucible. 
A  wire   stand   for   the   crucible 
about  |  the  height  of  the  bell. 
A  straight,  stiff,  iron  wire,  longer 

than  the  height  of  the  bell. 
A  candle  on  a  bent  wire. 
Materials  : 

Phosphorus  under  water.     (Dangerous! 

tongs.) 

Support  a  crucible  on  a  wire  stand  in  a  basin,  glass  trough,  or 
sink  containing  water.  Dry  a  small  piece  of  phosphorus  on  filter 
paper  and  transfer  to  the  crucible  with  tongs.  Invert  the  open 


FIG.  24.  —  Apparatus  for  Ex- 
periment 27.  Removing 
the  oxygen  from  the  air  by 
burning  phosphorus. 


Handle  only  with 


44 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


FIG.   25.  —  Candle 
on  bent  wire. 


bell  glass  over  the  crucible.  Heat  the  iron  wire  in  a  flame,  touch 
it  to  the  phosphorus,  immediately  withdraw  the  wire  from  the 
bell  and  insert  the  stopper.  The  water  in  the  basin  should  be 
deep  enough  to  prevent  the  escape  of  any  air 
on  account  of  the  expansion  due  to  the  burn- 
ing. Allow  to  stand  until  the  fumes  have  set- 
tled and  the  glass  has  cooled  to  the  room 
temperature  (10  or  15  minutes),  pouring  suffi- 
cient water  into  the  basin  from  time  to  time  to 
keep  the  inner  and  outer  levels  equal.  Remove 
the  stopper  and  lower  into  the  bell  (a)  a  lighted 
candle,  (b)  a  flaming  splint. 

Compare  the  results  with  those  obtained  with 
air  and  with  nitrogen  in  Experiment  26. 

Experiment  28. 

Fill  a  wide-mouthed  bottle  with  water  and 
pour  out  the  water  into  a  graduated  cylinder. 
Note  the  quantity  of  water  (number  of  cubic 
centimeters)  and  pour  it  back  into  the  bottle  in 
five  equal  portions,  marking  the  level  of  each 
fifth  with  a  label.  Cover  the  full  bottle  tightly  with  a  glass  plate, 
and  invert  it  into  a  trough  of  water.  Deliver  oxygen  into  the 
bottle  until  one-fifth  of  the  water  is  displaced.  Displace  the  re- 
maining four-fifths  similarly  with  nitrogen.  Again  cover  the 
mouth  of  the  bottle  with  the  glass  plate,  and  turn  the  bottle  over 
several  times  to  mix  the  gases.  Test  this  mixture  with  a  lighted 
splint  or  a  lighted  candle,  comparing  the  result  with  those  ob- 
tained in  Experiment  26. 

Experiment  29. 

Apparatus : 
Pan. 
Candle. 

Wide-mouthed  bottle. 

Attach  a  candle  to  the  bottom  of  a  pan,  and  cover  the  bottom 
of  the  pan  with  water.  Light  the  candle,  and  invert  over  it  the 
wide-mouthed  bottle  divided  into  fifths  (Expt.  28).  Is  the  flame 
extinguished  immediately?  After  a  time?  Allow  to  stand  until 
cool.  How  much  has  the  air  decreased  in  volume? 

Invert  pan  and  bottle  over  a  sink,  allowing  the  water  in  the  pan 
to  fall  out.  Remove  the  pan  and  immediately  test  the  gas  in 


JOSEPH  PRIESTLEY.  — 1733-1804. 

An  English  Unitarian  minister,  accredited  with  the  discovery  of  oxygen 
(1774),  because  he  was  the  first  to  describe  the  pure  substance.  Persecuted  in 
England  for  his  religious  and  political  views,  Priestley  emigrated  to  the  United 
States,  settling  in  Northumberland,  Pennsylvania,  where  he  spent  the  last  ten 
years  of  his  life. 


COMBUSTION 


45 


the  bottle  with  a  flaming  splint  or  candle.     Which  of  the  two  air 
gases  was  left  in  the  bottle  ? 


FIG.  26.  —  Experiment  29. 
Burning  a  candle  in  a 
bottle  of  air. 


FIG.  27.  —  Experiment  29. 
Inverting  the  bottle  to  ex- 
amine the  residual  gas. 


When  a  splint  or  candle  or  any  fuel  substance  is  burned 
in  air,  the  oxygen  of  the  air  disappears  and  the  nitrogen 
remains.  We  must  next  inquire  what  becomes  of  the  oxygen. 

Experiment  30. 

Materials  : 
Candle. 
Wide-mouthed  bottle. 

Over  a  lighted  candle  invert  a  dry,  cold,  wide-mouthed  bottle. 
Note  the  mist  which  gathers  on  the  inside  of  the  bottle.  This 
consists  of  droplets  of  water.  Cover  the  bottle,  turn  it  right  side 
up,  pour  in  a  little  limewater,  and  shake.  What  gas  must  have 
been  formed  in  the  combustion  of  the  candle  ? 

What  products  are  formed  in  the  combustion  of  illuminating 
gas?  (See  Expt.  12.) 

When  a  candle  burns,  it  obviously  loses  weight.  But 
we  have  just  seen  that  the  gases,  steam  and  carbon  dioxide, 
are  products  of  the  combustion.  In  open-air  combustion 
these  gases  are  constantly  being  swept  away  from  the  burn- 
ing substance  by  the  air  currents.  It  will  be  interesting  to 
examine  whether,  when  these  gases  are  retained  and  weighed 
along  with  the  diminished  candle,  there  has  been  any  loss 
of  weight.  The  following  experiment  determines  this  point. 


46 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


Experiment  31.* 

Apparatus : 

Balance. 

Sodium  hydroxide  in  sticks. 

Two  lamp  chimneys  or  open  glass  cylinders. 

Candle. 

Wire  gauze. 

Close  the  lower  ends  of  the  lamp  chimneys  with  wire  gauze, 
and  fill  them  with  approximately  equal  quantities  of  sodium 
hydroxide,  a  substance  which  will  take  up  both  the  water  and  the 
carbon  dioxide.  Attach  the  candle  to  a  card  or  flat  cork,  and  fix 
it  beneath  one  of  the  cylinders  of  caustic  soda.  Suspend  the 


FIG.  28.  —  Experiment  31.     Comparing  the  weight  of  an  unburned  candle  with 
that  of  a  burning  candle  and  the  products  of  its  combustion. 

chimneys  from  the  hooks  of  the  balance  and  counterpoise  the 
balance,  e.g.  with  sand.  Light  the  candle,  and  note  whether  the 
system  becomes  lighter  or  heavier  when  the  products  of  the 
combustion  are  not  allowed  to  escape.  Account  for  the  fact  that 
the  weight  does  not  remain  unchanged. 

Burning  in  an  abundant  supply  of  oxygen,  the  elements 
carbon  and  hydrogen,  respectively,  combine  with  oxygen, 
forming  carbon  dioxide  and  water.  These  same  products 


COMBUSTION  47 

are  formed  in  the  combustion  of  all  compounds  of  carbon 
and  hydrogen,  and  of  all  compounds  of  carbon,  hydrogen, 
and  oxygen.  No  other  products  than  carbon  dioxide  and 
water  are  formed  unless  (i)  other  elements  are  present,  or 
(2)  the  conditions  are  such  that  the  combustion  is  not  com- 
plete. Carbon  dioxide  and  water  vapor  are  not  poisonous. 
They  are  present  in  small  quantities,  even  in  the  purest  of 
outdoor  air.  On  the  other  hand,  the  products  of  combustion 
of  some  of  the  other  elements,  e.g.  sulphur  and  arsenic,  are 
injurious  to  the  health,  and  so  also  are  some  of  the  products 
of  incomplete  combustion  of  carbon  and  of  compounds  of 
carbon  and  hydrogen,  or  of  carbon,  hydrogen,  and  oxygen. 
The  most  dangerous  of  these  poisons  is  the  colorless  gas, 
carbon  monoxide,  CO,  which  has  the  property  of  combining 
with  that  constituent  of  the  blood  (hemoglobin)  whose 
function  it  is  to  take  up  oxygen  in  the  lungs  and  convey  it 
to  other  parts  of  the  body.  Hemoglobin  which  has  com- 
bined with  carbon  monoxide  cannot  combine  with  oxygen. 
Hence,  carbon  monoxide  poisoning  completely  deranges  the 
respiration  and  quickly  produces  fatal  results.  It  is  impor- 
tant that  the  student  of  household  science  should  have  some 
knowledge  of  this  poisonous  gas. 

Experiment  32.* 

Apparatus: 

Carbon  dioxide  generator. 

Iron  tube. 

Furnace  (see  Fig.  29). 

3  Woulff  bottles. 

Pneumatic  trough. 

Glass  cylinder. 

Connections. 
Materials : 

Charcoal  in  lumps. 

Potassium  hydroxide,  30  per  cent  solution. 
Pass  a  slow  current  of  carbon  dioxide  into  a  train  of  apparatus 
comprising  (i)  a  Woulff  bottle  containing  concentrated  sulphuric 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


acid,  (2)  an  iron  tube  packed  with  charcoal  and  heated  to  redness 

in  a  furnace,  (3)  2  Woulff 
bottles  containing  30  per  cent 
potassium  hydroxide,  (4)  a 
delivery  tube  leading  to  a 
cylinder  of  water  inverted  in 
a  pneumatic  trough.  (See 
Figure  29.)  The  carbon  di- 
oxide gas  from  the  generator 
is  dried  by  bubbling  through 
the  sulphuric  acid.  That 
part  of  the  gas  which  is  not 
acted  upon  by  the  red-hot 
carbon  in  the  iron  tube  is 
absorbed  by  the  potassium 
hydroxide  solution  in  the  two 
Woulfif  bottles.  The  carbon 
monoxide  gas  is  formed  by 
the  action  of  the  carbon  on 
the  carbon  dioxide,  thus : 

CO2  +  C  =  2  CO 

and  this  gas  passes  over  into 
the  pneumatic  trough,  where 
it  is  collected  by  displace^ 
ment  of  water. 

Reject  the  first  two  or 
three  cylinders  of  the  col- 
lected gas,  this  being  in  part 
the  air  originally  present  in 
the  apparatus.  Test  the  gas 
subsequently  collected  by 
applying  a  burning  splint. 
Note  the  color  of  the  flame. 
When  the  gas  is  all  burnt, 
pour  a  little  calcium  hydrox- 
ide solution  (limewater)  into 
the  cylinder,  and  shake. 
What  gas  is  formed  in  the 
combustion  of  carbon  mon- 
oxide ? 


COMBUSTION  49 

Carbon  monoxide  is  formed  in  coal  stoves  and  furnaces, 
and  burns  with  a  blue  flame  at  the  top  or  back  of  the  fire, 
where  it  meets  with  more  air.  Some  of  the  carbon  dioxide 
formed  at  the  bottom  of  the  fire  is  "  reduced  "  (the  word 
reduced  is  used  in  chemistry  in  the  sense  of  "  deprived 
of  oxygen  ")  to  carbon  monoxide,  by  the  red  hot  carbon 
of  the  fire,  just  as  carbon  dioxide  was  reduced  to  carbon 
monoxide  in  our  experiment.  If  the  draft  is  poor,  some 
of  this  poisonous  gas  may  escape  from  the  stove  and  con- 
taminate the  air  of  the  house.  It  requires  only  J  to  J  per 
cent  of  carbon  monoxide  in  the  air  of  a  room  to  have  a 
fatal  effect  upon  the  human  occupants  if  they  remain  exposed 
to  it  for  any  considerable  length  of  time,  and  even  -^  per 
cent  is  decidedly  injurious.  Inhaled  in  small  quantities, 
carbon  monoxide  causes  dullness,  sleepiness,  and  headache. 
Being  odorless  and  stupefying,  it  is  a  very  insidious  poison. 
Fortunately,  odorous  gases  usually  escape  with  it,  and 
these  may  suggest  its  possible  presence  to  one  on  the  lookout 
for  it.  Persons  poisoned  with  the  gas  should  be  immedi- 
ately taken  into  the  open  air  and  made  to  breathe  deeply. 
In  the  event  of  unconsciousness  or  stupefaction  artificial 
respiration  should  be  established,  as  in  the  treatment  for 
drowning.  This  consists  in  alternately  extending  the  arms 
above  the  head  and  pressing  them  firmly  against  the  chest. 

An  easier  but  less  instructive  way  of  preparing  carbon 
monoxide  depends  upon  the  so-called  dehydrating  action 
of  concentrated  sulphuric  acid.  In  Experiment  32  con- 
centrated sulphuric  acid  was  used  to  dry  the  carbon  dioxide, 
i.e.  to  take  up  the  water  vapor  mixed  with  the  gas.  Now, 
concentrated  sulphuric  acid  not  only  takes  up  free  water 
molecules,  as  in  the  above  instance,  but  actually  breaks 
up  many  molecules  by  withdrawing  the  elements  of  water 
from  them.  Formic  acid,  H2CO2,  is  one  of  the  substances 
which  is  decomposed  in  this  way  by  sulphuric  acid.  If  we 
examine  the  formula  of  formic  acid,  we  see  that  the  removal 
E 


50  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

of  a  molecule  of  water  from  a  molecule  of  formic  acid  leaves 
a  molecule  of  carbon  monoxide. 

H2CO2  =  H2O  +  CO 

Carbon  monoxide  may,  therefore,  be  prepared  as  follows: 


FIG.  30.  —  Experiment  33.     A  pparaius  for  ttie  generation  of  carbon 
monoxide  from  formic  acid. 

Experiment  33.* 

Materials  : 

Formic  acid  solution  (or  a  strong  solution  of  sodium  formate). 
Crude  sulphuric  acid. 
Apparatus : 

Flask  provided  with  a  dropping  funnel  and  a  delivery  tube. 
Pneumatic  trough. 
Cylinders  or  bottles. 
Connections. 

Allow  the  formic  acid  or  sodium  formate  solution  to  drop  slowly 
upon  the  concentrated  sulphuric  acid,  and  collect  the  gas  by  dis- 
placement of  water. 


CHAPTER  X 
THE   RELATION   OF   COMBUSTION   TO   HEAT 

HEAT  is  not  a  substance  in  the  sense  in  which  the  word 
substance  is  used  in  chemistry.  If  we  weigh  a  body  cold 
(say  a  platinum  crucible),  then  heat  it  and  weigh  it  again, 
we  find  that  in  spite  of  the  addition  of  heat  there  is  no  increase 
of  weight.  Had  we  added  any  substance  to  the  platinum, 
the  weight  would  have  increased.  There  is  no  molecule 
of  heat.  On  the  contrary,  heat  is  regarded  as  consisting  in 
molecular  motion,  the  molecules  of  hot  bodies  vibrating 
back  and  forth  more  rapidly  than  those  of  cold  bodies.  (See 
Chapter  VI.)  That  mechanical  work  or  energy  can  be  con- 
verted into  heat  is  illustrated  by  the  primitive  methods  of 
obtaining  fire  practiced  by  savage  races,  such  as  the  rubbing 
together  of  two  sticks  of  wood,  or  the  twirling  of  one  stick 
upon  a  hollowed  part  of  a  second  stick.  The  same  prin- 
ciple was  demonstrated  on  a  larger  scale  in  1798  by  Count 
Rumford,  who,  by  an  experiment  performed  publicly  before 
the  Elector  of  Bavaria,  showed  that  in  boring  a  cannon  with 
a  blunt  borer  it  is  possible  to  heat  over  25  pounds  of  water  to 
the  boiling  point  in  about  two  hours  and  a  half. 

That,  conversely,  work  can  be  obtained  from  heat  is 
illustrated  by  the  steam  engine,  which  is  a  machine  devised 
for  that  very  purpose. 

Heat  is  therefore  a  form  of  energy,  and  the  study  of  heat 
belongs  to  the  domain  of  physics.  On  account  of  its  relation 
to  combustion,  however,  it  is  desirable  that  we  have  clear 
conceptions  of  the  meanings  of  some  words  relating  to  heat. 

Temperature  is  a  familiar  term.  A  hot  body  is  said  to 
have  a  high,  and  a  cold  one,  a  low  temperature.  Instruments 


52  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

used  to  measure  temperature  are  called  thermometers.  Two 
styles  of  thermometers  are  in  common  use  in  America  — 
the  Fahrenheit  and  the  Centigrade,  or  Celsius.  Placed  in 
melting  ice  or  in  freezing  water  the  Fahrenheit  thermometer 
registers  32  degrees;  the  Centigrade  thermometer,  zero. 
Placed  in  the  vapor  of  boiling  water  the  Fahrenheit  ther- 
mometer registers  212  degrees;  the  Centigrade,  100  degrees. 
Thus  the  interval  between  the  freezing  and  boiling  points  of 
water  is  divided  on  the  Fahrenheit  thermometer  into  180 
degrees,  and  on  the  Centigrade  thermometer  into  100  degrees. 
In  other  words,  100  Centigrade  degrees  =  180  Fahrenheit 
degrees,  or  i  Centigrade  degree  =  1.8  Fahrenheit  degrees. 

The  quantity  of  heat  in  a  body  depends  not  only  on  its 
temperature,  but  also  on  its  mass  and  on  the  substance  of 
which  it  is  composed.  Thus,  while  a  cupful  of  boiling  water 
and  a  barrelful  of  boiling  water  have  exactly  the  same  tem- 
perature they  contain  very  different  quantities  of  heat. 
Instruments  used  to  measure  quantity  of  heat  are  known  as 
calorimeters.  (See  p.  55.) 

Various  units  of  quantity  of  heat  have  been  proposed. 
We  shall  define  two  —  the  Calorie  ("  large  calorie "  or 
"  kilogram  calorie  "  *)  and  the  British  Thermal  Unit  (B.  T.  U.). 

A  Calorie  is  the  quantity  of  heat  that  will  raise  the  tem- 
perature of  one  kilogram  of  water  one  degree  Centigrade. 

A  British  Thermal  Unit  is  the  quantity  of  heat  that  will  raise 
the  temperature  of  one  pound  of  water  one  degree  Fahrenheit. 

A  Calorie  is  approximately  equal  to  4  British  Thermal 
Units.2 


*A  "small"  or  "gram"  calorie  is  the  quantity  of  heat  that  will  raise  the 
temperature  of  one  gram  of  water  one  degree  Centigrade.  One  Calorie  (spelled 
with  a  capital)  is  therefore  equal  to  1000  calories  (spelled  with  a  small  c).  It 
should  be  noted,  however,  that  in  books  in  which  there  is  no  reference  to  small 
calories  the  large  calorie  may  be  found  spelled  without  the  capital. 
2  i  Kilogram  =  2.2  Ib. 

i  Centigrade  degree  =  1.8  Fahrenheit  degrees. 
;.  i  Calorie  =  2.2  X  1.8  =  3.96  B.T.U. 


SIR  BENJAMIN  THOMPSON,  COUNT  RUMFORD.— 1753-1814. 

Who  demonstrated  the  production  of  heat  by  friction.  Born  at  Woburn, 
Massachusetts,  Thompson  removed  to  England  early  in  the  War  of  Independ- 
ence and  later  returned  in  command  of  British  troops,  which  did  not  see  ac- 
tive service.  In  1783  he  entered  the  service  of  the  Elector  of  Bavaria,  be- 
coming a  minister  of  state.  For  his  services  to  Bavaria  he  was  created  a 
Count  of  the  Holy  Roman  Empire,  his  title  of  Rumford  being  derived  from 
the  New  Hampshire  town  (now  Concord),  where  he  had  taught  school.  Re- 
turning to  England  in  1795,  he  projected  the  Royal  Institution  and  selected 
Sir  Humphry  Davy  as  its  first  scientific  lecturer.  The  last  ten  years  of  his 
life  were  spent  in  France,  where  he  married  the  widow  of  the  great  French 
chemist,  Lavoisier.  Amongst  his  numerous  interests  Rumford  devoted  much 
attention  to  problems  of  cooking,  clothing,  and  fuel  economy. 


THE    RELATION    OF    COMBUSTION   TO   HEAT        53 

Ignition  Temperature 

Experiment  34. 

Materials : 

Disks  of  sheet  iron  or  tinned  iron  4  inches  in  diameter. 
Coke,  charcoal,  yellow  phosphorus  (under  water),  red  phos- 
phorus, sulphur,  pine,  and  soft  coal. 
Forceps  to  handle  the  yellow  phosphorus. 
Filter  paper  to  dry  the  yellow  phosphorus. 
At  equal  distances  from  the  center  of  a  circular  piece  of  metal, 
e.g.  the  cover  of  a  tin,  supported  on  a  tripod  or  an  iron  ring,  place 
small  portions  of  coke,  charcoal,  red  phosphorus,  yellow  phos- 
phorus, sulphur,  pine,  and  soft  coal.     Place  a  Bunsen  flame  exactly 
under  the  center  of  the  metal,  and  note  the  order  in  which  the 
materials  take  fire. 

It  is  a  familiar  fact  that  most  substances  must  be  heated 
before  they  will  burn,  and  that  some  substances  must  be 
made  much  hotter  than  others.  Everybody  knows,  for 
instance,  that  anthracite  coal  (hard  coal)  cannot  be  ignited 
as  easily  as  pine  wood.  Every  substance  may  be  said  to  have 
its  ignition  temperature.  Thus,  while  some  kinds  of  dry 
peat  will  ignite  at  200°  C.,  and  charcoal  in  pure  oxygen 
ignites  at  345°  C.,  graphite  will  not  take  fire  below  690°  C. 
in  pure  oxygen,  nor  diamond  below  800°  C.  (Charcoal, 
graphite,  and  diamond  are  three  modifications  of  the  element 
carbon.)  A  few  substances  will  ignite  at  ordinary  atmos- 
pheric temperatures,  but  such  are  rare  and  unimportant. 

Matches  are  tipped  with  substances  of  ignition  tempera- 
tures sufficiently  low  to  be  attained  by  friction.  Yellow 
phosphorus,  covered  with  a  protective  coating,  has  been  much 
used  for  this  purpose,  but  is  now  prohibited  in  most  civilized 
countries,  on  account  of  its  injurious  effects  upon  the  health 
of  the  factory  operatives.  Red  phosphorus  is  free  from  this 
objection,  and  so  is  the  compound  phosphorus  pentasul- 
phide,  P2SB.  Matches  can  also  be  made  without  any  phos- 
phorus. Indeed,  the  earliest  friction  matches  (known  as 


54  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

lucifer  matches  or  "  Congreves " x)  were  tipped  with  a 
phosphorus-free  mixture,  consisting  of  antimony  sulphide, 
potassium  chlorate,  starch,  and  gum. 

Safety  matches  are  tipped  with  a  mixture  that  is  difficult 
to  ignite  by  simple  friction,  but  which  ignites  when  rubbed 
upon  a  second  mixture  (containing  red  phosphorus)  which 
is  applied  to  the  surface  of  the  match  box. 

Heat  of  Combustion 

The  heat  of  combustion  of  a  substance  is  the  quantity 
of  heat  produced  when  a  given  quantity  (one 
pound  or  one  gram)  of  the  substance  is  com- 
pletely oxidized.  The  heat  of  combustion  of  any 
substance  is  always  the  same  whether  the  sub- 
stance burns  rapidly,  e.g.  in  compressed  pure 
oxygen,  or  more  slowly,  as  in  air ;  or  even  oxi- 
dizes slowly  without  the  phenomena  of  combus- 
tion. The  temperature  attained  during  the  oxi- 
dation is,  however,  greater  the  more  rapidly  the 
substance  burns. 

Experiment  35.* 

Materials : 

Bottle  of  oxygen. 

Small  pieces  of  yellow  phosphorus  in  a  dish  of 

water. 

Deflagrating  spoon. 
Forceps. 
Porcelain  dish. 

With  the  forceps  remove  one  piece  of  phosphorus 
from   the    water,    place   it  on  filter   paper  for  a 
moment  to  dry,  then  leave  it  in  the  dry  porcelain 
^deflagrating     ^sh  exPose(i to  tne  air-     Dry  a  second  piece,  transfer 
spoon.  it  to  the  deflagrating  spoon,  and  ignite  it  by  warming. 

Dry   a   third  piece,    ignite  it  in   the  deflagrating 
spoon,  and  immediately  plunge  it  into  the  oxygen. 

1  So  named  by  the  inventor,  John  Walker,  in  1827,  in  honor  of  Sir  William 
Congreve. 


THE    RELATION    OF    COMBUSTION   TO    HEAT        55 


In  the  experiment  just  performed  the  higher  temperature 
attained  in  the  more  rapid 
combustion  is  made  ap- 
parent by  the  greater  bril- 
liance and  smaller  volume 
of  the  flame.  Careful  ex- 
periment with  a  calorimeter 
shows  that  the  quantity  of 
heat  set  free  in  the  oxida- 
tion of  a  given  amount  of 
phosphorus  is  identical  in 
the  three  instances.  But 
the  same  quantity  of  heat, 
set  free  in  a  smaller  space 
and  at  a  more  rapid  rate, 
produces  a  higher  tempera- 
ture. 

To  measure  heats  of  com- 
bustion accurately  the  com- 
bustion is  caused  to  take 
place  as  rapidly  as  possible, 
and  the  heat  produced  is 
used  to  heat  water.  To 
this  end  a  weighed  quantity 
of  the  substance,  whose 
heat  of  combustion  is  to 
be  determined,  is  burned 
in  compressed  oxygen  in  a 
steel  bomb.  (See  Fig.  32.) 
The  bomb  is  immersed  in 
a  vessel  of  water,  into  which 
a  thermometer  dips.  The 
heat  produced  in  the  com- 
bustion heats  the  water  surrounding  the  bomb.  Knowing 
the  weight  of  this  water,  and  how  much  its  temperature  is 


FIG.  32.  —  A  bomb  calorimeter.  Th« 
substance  in  the  bomb  is  ignited  by 
an  electrical  device.  The  platinum 
wires,  H  and  /,  the  former  of  which 
is  insulated  from  the  steel  of  the  bomb, 
are  connected  inside  the  bomb  by  a 
little  coil  of  iron  wire  just  above  the 
capsule,  O,  which  contains  the  sub- 
stance to  be  burned.  An  electric 
current,  passed  through  these  wires 
for  a  few  seconds,  heats  the  iron  wire 
to  redness,  when  it  burns,  and,  falling 
on  the  substance  in  the  capsule,  sets 
it  on  fire.  S  in  the  figure  is  a  stirrer, 
which  is  kept  in  constant  motion  to 
keep  the  water  well  mixed. 


56  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

raised,  we  can  easily  calculate  the  number  of  calories  or 
British  Thermal  Units  of  heat  that  have  gone  into  it.  If, 
for  instance,  2  pounds  of  water  have  been  heated  2  Fahren- 
heit degrees,  we  know  that  2X2  =  4  B.  T.  U.  must  have 
gone  into  the  water. 

When  12  pounds  of  carbon  (one  atomic  weight  in  pounds) 
are  burned  to  carbon  dioxide,  174,500  B.  T.  U.  are  set  free. 
When  the  quantity  of  carbon  monoxide  containing  12 
pounds  of  carbon  (viz.  28  pounds)  is  burned,  122,400  B.  T.  U. 
are  set  free.  From  this  we  infer  that  when  12  pounds  of 
carbon  are  burned  to  carbon  monoxide,  only  52,100  B.  T.  U. 
are  liberated.  In  other  words,  any  carbon  monoxide  allowed  to 
escape  up  the  chimney  unburned  involves  a  loss  of  more  than 
two- thirds  of  the  heat  the  carbon  contained  in  it  was  capable 
of  yielding.  It  is,  therefore,  bad  economy  to  have  the  upper 
part  of  a  coal  stove  or  furnace  so  tightly  closed  that  air 
cannot  enter  to  burn  the  carbon  monoxide.  Moreover,  if  the 
carbon  monoxide  is  not  burned,  there  is  danger  that  some 
of  this  extremely  poisonous  gas  may  escape  into  the  room. 
A  blue  flame  on  the  top  of  a  coal  fire  is  evidence  that  the 
carbon  monoxide  is  burning. 


Propagation  of  Combustion 

Fire  once  started  has  a  tendency  to  spread.  This  is 
because,  once  a  portion  of  the  combustible  substance  is  in 
active  combustion,  the  heat  set  free  raises  neighboring 
portions  to  the  kindling  point.  In  solid  and  liquid  fuels 
burning  with  a  flame,  a  part  of  the  heat  produced  by  the  com- 
bustion is  used  in  converting  the  solid  or  liquid  into  the 
gaseous  condition.  In  gases  all  the  heat  is  available  for  the 
ignition  of  new  portions  of  the  gas.  If  the  combustible  gas 
is  mixed  with  sufficient  air  to  provide  all  or  nearly  all  the 
oxygen  necessary  to  burn  it,  an  explosion  takes  place.  This 
is  because  the  combustion  spreads  almost  instantaneously. 


THE   RELATION  OF   COMBUSTION  TO  HEAT          57 

An  enormous  quantity  of  heat  is  consequently  liberated  in 
an  instant.  Gases  tend  to  expand  when  heated.  If  they 
are  confined  within  an  inclosed  space  (such  as  a  bottle  or 
even  a  room) ,  they  exert  a  pressure  on  trie  walls  of  the  space 
in  consequence  of  this  tendency  to  expand.  If  the  pressure 
is  sufficiently  great,  the  walls  of  the  inclosing  vessel  or  room 
may  be  shattered. 

When  gas  has  been  escaping  into  a- room  or  oven,  there  is 
always  a  possibility  that  it  may  be  mixed  with  the  air  in 
explosive  proportions.  It  is,  therefore,  extremely  dangerous 
to  bring  a  light  into  the  room  or  near  the  oven  until  the  gas 
has  been  shut  off  and  the  room  or  oven  well  ventilated. 
Vessels  containing  volatile  l  liquids  such  as  gasoline  and 
benzine  are  apt  to  have  explosive  mixtures  in  the  space  above 
the  liquid.  Such  liquids  should  not  be  used  for  cleaning  pur- 
poses in  a  room  in  which  a  lamp  or  fire  is  burning.  Explo- 
sions have  been  known  to  occur  when  benzine  was  used 
many  feet  from  a  flame. 

Finely  divided  solid  or  liquid  combustibles  may  also 
form  explosive  mixtures  with  air.  Explosions  of  coal  dust 
and  of  flour  dust  are  not  uncommon  in  the  air  of  mines  and 
mills. 

Gas  and  gasoline  engines  derive  their  power  from  the 
explosive  combustion  of  mixtures  of  air  with  combustible 
gases  and  minute  droplets  of  combustible  liquids. 

Spontaneous  Combustion 

Oxidation  of  many  substances  occurs  slowly  at  tem- 
peratures below  their  ignition  points.  Phosphorus,  for  exam- 
ple, oxidizes  slowly  but  completely  at  ordinary  room  temper- 
ature, although  its  ignition  point  is  considerably  higher. 
Iron  oxidizes  slowly  in  moist  air,  and,  curiously  enough, 
combines  with  more  oxygen  than  when  it  is  burned  in  pure 

1 A  volatile  liquid  is  one  which  is  readily  converted  into  vapor  or  gas. 


58  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

or  even  in  compressed  oxygen.  Linseed  oil,  exposed  to  the 
air  in  thin  layers,  as  when  used  in  paint,  oxidizes  partially, 
yielding  a  solid  film.  The  "  drying  "  of  paint  is  due  to  this 
reaction  rather  than  to  the  evaporation  of  any  liquid. 

We  have  learned  that  when  slow  oxidations  such  as  these 
occur  the  quantity  of  heat  set  free  is  the  same  as  if  they 
occurred  rapidly.  Now  if  the  oxidation  goes  on  at  such  a 
rate  that  heat  is  produced  a  little  more  rapidly  than  it  is 
conveyed  away  from  the  oxidizing  body,  it  is  evident  that 
the  latter  will  gradually  become  warmer.  This  will  cause 
the  rate  of  oxidation  to  become  greater ;  heat  will  therefore 
be  liberated  more  rapidly  than  before ;  and  the  temperature 
of  the  oxidizing  body  will  continue  to  go  up,  until  finally 
the  ignition  temperature  is  attained  and  the  substance  bursts 
into  active  combustion.  Spontaneous  combustion  has  been 
observed  in  stored  coal,  in  cotton  waste  wet  with  oil,  in  hay, 
and  in  other  materials. 


CHAPTER  XI 
FUELS 

FUELS  are  conveniently  classified  according  to  their  physi- 
cal state,  thus : 

1.  Solid  Fuels.  —  Wood,  peat,  the  several  varieties  of  coal, 
charcoal,  coke. 

2.  Liquid  Fuels.  —  Alcohol,  wood  alcohol,  gasoline,  kerosene 
(coal  oil),  "  fuel  oil,"  crude  petroleum. 

3.  Gaseous  Fuels.  —  Natural  gas,  coal  gas,  water  gas,  producer 
gas,  air  gas  (or  gasoline  gas),  oil  gas,  acetylene. 

These  all  contain  carbon,  and  all  but  charcoal  and  coke 
contain  hydrogen.  Most  of  them  are  mixtures  of  different 
substances,  e.g.  coal  gas  of  free  hydrogen,  carbon  monoxide, 
and  methane  (CELO ;  water  gas  of  free  hydrogen,  carbon 
monoxide,  and  nitrogen;  etc.  The  solids  and  most  of 
the  gases  contain  more  or  less  incombustible  matter.  In  the 
gases  this  consists  usually  of  free  nitrogen,  free  oxygen, 
argon,  and  carbon  dioxide ;  in  the  solids,  of  oxides  and  salt- 
like  compounds  of  the  metals.  The  incombustible  gases,  of 
course,  pass  up  the  chimney  with  the  carbon  dioxide  and 
steam  produced  in  the  combustion.  The  incombustible 
solids,  for  the  most  part,  remain  as  ashes,  though  the  smaller 
particles  may  be  swept  away  into  the  chimney  with  the 
gases. 

As  the  hot  gases  from  a  fire  cool,  the  water  and  some  of 
the  products  of  incomplete  combustion  condense,  i.e.,  change 
from  the  gaseous  to  the  liquid  form,  and  the  minute  droplets 
so  formed,  together  with  the  particles  of  ash,  constitute 
the  white  matter  of  smoke.  Some  of  the  oily  products  of 
incomplete  combustion  which  are  most  easily  condensed, 

59 


6o  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

and  some  of  the  carbon  and  ash  lodge  in  the  chimney  or 
pipes,  and  the  mixture  constitutes  soot.  The  oily  matter  of 
soot,  sometimes  spoken  of  as  "  oil  of  smoke,"  is  a  complex 
mixture  of  compounds  analogous  to  carbolic  acid. 

Solid  Fuels 

Wood.  —  The  hard  woods  are  most  valued  for  fuel  pur- 
poses. These  all  come  from  deciduous  trees  —  trees  which 
shed  their  foliage  annually.  Those  most  used  as  fuel  may 
be  placed  in  the  following  approximate  order  of  merit, 
though  it  must  be  remembered  that  there  are  many  varieties 
of  each  species  and  that  these  have  unequal  merit :  hickory, 
oak,  ash,  sugar  maple,  black  maple,  beech,  birch. 

The  evergreen  conifers  and  some  of  the  deciduous  trees 
yield  soft  woods,  which  ignite  readily  and  are  therefore 
particularly  useful  as  kindling  for  harder  wood  and  for  coal. 
Soft  woods  may  also  be  used  for  fuel  proper.  The  most 
valuable  soft-wood  fuels  are  those  from  the  conifers :  pine, 
spruce,  hemlock,  cedar,  sequoia,  and  redwood. 

Wood  consists,  in  the  main,  of  compounds  of  carbon, 
hydrogen,  and  oxygen  —  largely  cellulose  and  closely  related 
substances,  having  an  average  composition  roughly  rep- 
resented by  the  formula,  C6Hi0O5,  i.e.  C,  44.4  per  cent; 
H,  6.2  per  cent ;  O,  49.4  per  cent. 

Mixed  with  these  compounds  there  is  always  a  considera- 
ble quantity  of  water  and  some  incombustible  "  mineral  " 
matter,  i.e.  ash.  The  conifer  woods  also  contain  turpentine 
and  resins,  consisting  of  compounds  of  carbon  and  hydrogen, 
some  of  them  without  any  oxygen,  some  with  much  le< 
oxygen  than  is  contained  in  the  cellulose-like  compounds. 
These  substances  have  high  heats  of  combustion,  and  it  is 
their  presence  which  renders  the  conifer  woods  more  valuable 
for  fuel  than  the  soft  deciduous  woods  such  as  poplar,  willow, 
and  basswood. 

The  amount  of  water  in  the  wood  has  a  great  effect  on 


FUELS  6 i 

its  practical  calorific  value,  for  if  much  water  is  present,  a 
large  proportion  of  the  heat  is  used  in  vaporizing  (boiling) 
this  water. 

The  amount  of  water  in  the  wood  depends  upon  the  variety, 
upon  the  season  at  which  the  wood  is  cut,  and  upon  the 
seasoning.  Wood  cut  in  midwinter  contains  less  water  than 
that  cut  at  other  seasons.  No  wood  is  water-free  unless  it 
has  been  kiln-dried.  But  while  seasoned  wood  has  only  20 
per  cent  or  less  of  water,  green  wood  or  wet  wood  may  have 
as  much  as  50  per  cent.  Green  ash  contains  about  30  per 
cent,  green  poplar  about  50  per  cent,  of  water.  It  is  at  least 
partly  due  to  the  water  contained  even  in  air-dried  wood  that 
it  is  impossible  to  get  a  very  hot  fire  with  wood,  except  in 
tlie  later  stages  of  the  combustion.  At  that  time  the  water 
and  the  gases  produced  by  the  decomposition  have  been 
driven  off  and  the  fire  has  become  essentially  a  charcoal  fire. 

Weight  for  weight,  there  is  little  difference  in  the  calorific 
value  (i.e.  heat  of  combustion)  of  perfectly  dry  soft  woods 
and  perfectly  dry  hard  woods.  But  wood  is  bought  and 
sold  by  measure,  not  by  weight.  A  cord  of  dry  pine  — 
a  pile  8  feet  long,  4  feet  wide,  and  4  feet  high  —  is  said  to 
weigh  3000  pounds,  and  a  cord  of  dry  maple  from  4500  to 
5000  pounds.  Cord  for  cord,  then,  dry  hard  wood  has  a 
much  higher  calorific  power  than  soft  wood.  A  cord  of  hard 
wood  yields  about  the  same  quantity  of  heat  as  a  ton  of  coal, 
viz.  20  to  30  million  B.  T.  U. 

Soft  woods,  particularly  those  which  are  light  and  porous, 
not  only  ignite  more  readily,  but  also  burn  more  rapidly 
than  hard  woods.  They  thus  give  a  hot  fire,  but  one  which 
requires  constant  attention.  Hard  woods  produce  more 
charcoal  than  soft  woods,  and  of  a  better  quality.  This  is 
another  reason  why  a  hard-wood  fire  is  steadier  and  more 
persistent  than  one  of  soft  wood. 

The  ash  from  hard  wood  contains  potassium  carbonate, 
which  in  former  days  was  commonly  leached  out  and  used 


62  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

for  soap-making  and  other  purposes.  Hard- wood  ashes  have 
considerable  value  as  agricultural  fertilizers.  This  is  due 
to  the  compounds  of  potassium,  phosphorus,  and  calcium 
contained  in  them.  The  potassium  compounds  are  the  most 
important  in  this  respect,  and  since  these  are  soluble  in  water, 
ashes  which  have  been  leached,  either  intentionally,  as  in 
the  making  of  lye,  or  through  carelessness,  e.g.  by  exposure 
to  rain,  have  but  little  fertilizing  value.  Soft-wood  ashes, 
even  if  protected  from  leaching,  have,  as  a  rule,  very  little 
value  as  fertilizers. 

Peat  is  a  substance  produced  by  the  decay  under  water 
of  certain  swamp  plants,  particularly  mosses.  In  its  natural 
state  it  contains  more  water  than  even  green  wood.  It  is 
very  difficult  to  dry  below  a  moisture  content  of  30  to  50 
per  cent,  and  in  this  condition  its  calorific  value  is  little, 
if  any,  above  that  of  wood.  Better  drying  can,  however, 
be  accomplished  if  the  fiber  is  broken  up  by  mechanical 
treatment.  Peat  improved  by  such  processes  of  manufacture 
is  now  an  important  fuel  in  some  European  countries  and  is 
beginning  to  be  of  importance  in  Canada.  It  is  admirably 
adapted  to  domestic  use. 

Coal  is  a  general  name  given  to  the  solid  fuels  found  as 
minerals.  There  is  good  evidence  that  for  the  most  part 
these  have  been  formed  by  the  decay  of  plants  of  the  conifer, 
fern,  and  palm  families.  Under  varying  conditions  there 
have  been  formed  coals  showing  very  material  differences  in 
composition  and  physical  properties. 

Lignite  or  brown  coal  owes  its  name  (from  the  Latin 
lignum,  wood)  to  the  fact  that  it  often  shows  more  or  less 
clearly  the  structure  of  wood.  On  account  of  its  propensity 
to  break  up  into  powder  as  it  dries,  lignite  has  little  com- 
mercial value  except  in  the  immediate  neighborhood  of  its 
mines,  where  it  can  be  used  comparatively  soon  after  being 
brought  to  the  surface.  There  are  large  deposits  of  lignite 
in  the  western  regions  of  the  United  States  and  Canada, 


FUELS  63 

but  the  larger  part  of  the  western  coals  and  practically  the 
whole  of  the  eastern  fuels  fall  in  the  following  groups. 

Lignitic  coal  resembles  lignite  in  structure,  but  is  darker 
in  color,  contains  less  water,  and  is  more  stable.  In  compo- 
sition and  fuel  value  it  is  intermediate  between  true  lignite 
and  bituminous  coal.  Most  of  the  coals  found  in  the  great 
plains  and  a  considerable  part  of  those  found  in  the  far  West 
belong  to  this  class.  They  range  from  the  true  lignites, 
containing  say  20  per  cent  of  water,  down  to  the  lighter 
grades  of  bituminous  coal  which  contain  little  or  no  com- 
bined water.  Lignitic  coals  are  valuable  fuels. 

Lignitic  coal  with  18  per  cent  of  water  contains  about 
50  per  cent  of  carbon,  a  little  less  than  5  per  cent  of  hydrogen, 
and  1 6  per  cent  of  oxygen  and  nitrogen.  It  burns  with  a 
smoky  flame  and  yields  from  8000  to  11,000  B.T.  U.  per 
pound. 

Bituminous  or  soft  coal  contains  more  carbon  and  much 
less  oxygen  than  lignitic  coal,  and  has,  therefore,  a  higher 
calorific  value.  Some  varieties  (e.g.  Connellsville)  melt 
slightly  and  cake  in  burning ;  others  burn  without  caking. 
Some  burn  with  little,  others  (e.g.  Nova  Scotia)  with  much, 
flame  and  smoke.  It  is  from  bituminous  coal  of  medium 
grades  that  coke  and  coal  gas  are  best  manufactured. 
Bituminous  coal  contains  from  55  to  80  per  cent  of  carbon, 
and  from  1 5  to  50  per  cent  of  volatile  matter  (matter  driven 
off  as  gas  in  the  manufacture  of  coke).  The  caking  coals 
have  usually  less  oxygen  and  more  volatile  matter  than 
the  non-caking.  The  surface  of  a  caking  coal  fire  requires 
breaking  up  occasionally,  so  as  to  allow  free  draft  through 
the  fire.  Bituminous  coal  is  by  far  the  most  important  fuel 
in  North  America,  if  not  in  the  whole  world. 

Semi-bituminous  or  semi-anthracitic  coal  is  intermediate 
between  bituminous  coal  and  anthracite.  It  has  over  80 
per  cent  of  carbon  and  15  to  20  per  cent  of  volatile  matter. 
It  burns  with  a  shorter  flame  than  bituminous  coal,  but  may 


64  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

be  either  harder  or  softer.  An  example  of  this  kind  of  coal 
is  Pocahontas. 

Anthracite  or  hard  coal  is  the  densest  and  hardest  variety 
of  coal  and  contains  the  most  carbon  and  the  least  hydrogen, 
oxygen,  and  volatile  matter.  It  is  hard  to  kindle,  burns  with 
a  steady,  intense  heat,  produces  little  or  no  smoke,  and 
requires  less  frequent  attention  than  any  of  the  other  varieties. 
Anthracite  has  from  84  to  over  96  per  cent  of  carbon  and  but 
3  to  10  per  cent  of  volatile  matter. 

Good  grades  of  semi-bituminous  and  anthracite  coal  yield 
from  13,500  to  15,500  B.  T.  U.  per  pound. 

The  figures  given  above  for  the  composition  of  coals  of 
the  various  classes  refer  to  pure  air-dried  coals  with  a  mini- 
mum of  ash.  Commercially,  all  coals  contain  considerable 
quantities  of  dirt  and  mineral  impurity ;  and  coal  as  mined 
and  shipped  always  carries  some  moisture,  as  distinguished 
from  chemically  combined  water.  Perhaps  the  average  of 
all  coals  sold  would  contain  10  to  12  per  cent  of  ash  and 
1.5  to  2  per  cent  of  moisture.  The  amount  and  character 
of  the  ash  in  coal  is  an  important  practical  consideration. 
In  amount  it  ranges  from  3  to  20  per  cent,  with  extremes 
above  and  below.  Coals  containing  sulphur  are  more  likely 
to  give  clinkery  ashes  than  sulphur-free  coals.  Clinkers, 
accumulating  upon  the  grate  of  a  furnace  or  stove,  are  objec- 
tionable, not  only  because  they  are  apt  to  clog  the  shaking 
mechanism,  but  also  because  they  interfere  with  the  draft. 

Coal  ashes  have  much  the  same  composition  as  clay. 
They  have  practically  no  fertilizing  value. 

Charcoal  is  made  by  the  destructive  distillation  of  wood ; 
coke  by  that  of  bituminous  coal.  (See  Expts.  24  and  25.) 
They  both  consist  of  free  carbon  mixed  with  the  ash  constit- 
uents of  the  wood  or  coal  from  which  they  are  made.  Both 
burn  without  flame  (or  with  a  carbon  monoxide  flame  if  the 
fire  is  deep),  and  both  yield  about  13,000  B.  T.  U.  per  pound. 
Coke  is  of  two  kinds:  (i)  Furnace  or  metallurgical  coke, made 


FUELS  65 

in  so-called  "  coke  ovens  "  as  a  primary  product,  the  gas, 
tar,  etc.,  being  secondary  products  or  in  all  too  many  cases 
wasted ;  (2)  Gas  coke,  a  much  softer  material  left  in  the  retorts 
used  in  the  manufacture  of  illuminating  gas  from  coal. 
Gas  coke  is  a  valuable  domestic  fuel,  igniting  almost  as 
easily  as  bituminous  coal  and  burning  with  a  very  intense 
flameless  fire.  Furnace  coke,  on  the  other  hand,  is  a  very 
hard  substance  and  is  more  difficult  to  ignite  than  anthracite. 
While  of  great  industrial  importance,  this  kind  of  coke  is 
unsuitable  for  domestic  use. 

In  all  solid  fuel  fires,  and  especially  in  coal  fires,  it  is 
important  to  keep  the  grate  and  the  surface  of  the  fuel  free 
from  an  accumulation  of  ashes.  Ashes  not  only  impede  the 
draft  but,  covering  the  surface  of  the  fuel,  they  prevent 
the  oxygen  from  coming  in  contact  with  the  combustible 
solid.  The  shaking  of  the  fire  not  only  clears  the  grate  of 
the  ashes  which  tend  to  clog  it,  but  also  shakes  off  the  cover- 
ing of  ashes  from  the  face  of  the  coals  and  exposes  the  latter 
to  the  action  of  the  oxygen. 

For  further  information  about  solid  fuels  the  reader  is  referred  to 
Chapter  V  of  Benson's  "  Industrial  Chemistry"  (New  York,  1913)  and 
to  the  numerous  references  there  cited. 


CHAPTER  XII 

FUELS   (Continued] 

Liquid  Fuels 

THE  most  important  liquid  fuels  are  the  petroleum  prod- 
ucts —  especially  kerosene.  The  alcohols  are  at  present 
fuels  of  secondary  importance. 

Petroleum  is  an  oil  obtained  from  underground  sources. 
It  is  a  mixture  of  a  great  many  compounds  of  carbon  and 
hydrogen.  In  the  refining  process  the  more  volatile  com- 
pounds are  separated  from  those  less  volatile.  A  large 
number  of  products  are  thus  obtained. 

Benzine  and  gasoline  are  two  of  the  most  useful  of  the 
light  or  volatile  products;  kerosene  is  heavier  and  less 
volatile;  the  still  less  volatile  constituents  of  the  crude 
petroleum  make  up  such  products  as  lubricating  oils,  axle 
greases,  vaseline  (or  petrolatum),  and  paraffin  wax. 

The  vapor  of  benzine  and  gasoline  is  given  off  in  sufficient 
abundance  at  ordinary  temperatures  to  form  explosive 
mixtures  with  air.  On  account  of  this  danger  benzine  and 
gasoline  should  not  be  used  as  household  fuels. 

Kerosene  (called  "  paraffin "  in  England  and  "  coal 
oil  "  in  some  parts  of  America),  if  well  made,  gives  off  very 
little  vapor  at  ordinary  temperatures  —  enough  to  affect 
the  sense  of  smell,  but  not  nearly  enough  to  form  an  explo- 
sive mixture  with  air.  The  momentary  application  of  a 
flame,  either  above  or  directly  to  the  surface  of  the  cold  oil, 
will  cause  no  ignition.  The  flame  or  "  flash  "  test  commonly 
applied  to  kerosene  is  a  test  to  determine  to  what  temperature 
the  oil  must  be  heated  in  order  that  it  may  give  off  sufficient 

66 


FUELS 


67 


vapor  to  form  a  combustible  mixture  with  air.  The  laws  of 
most  countries  prescribe  a  minimum  flash  point  for  oils 
offered  for  sale  for  illuminating  purposes. 

Kerosene  stoves  are  of  two  types.  One  type  is  con- 
structed like  a  large  kerosene  lamp  and  gives  a  yellow,  sooty 
flame.  The  other  type  gives  a 
blue  flame  like  a  Bunsen  burner. 
In  the  lamp-like  stove  the  oil 
rises  from  the  reservoir  to  the 
burner  through  a  wick,  and  is 
converted  into  gas  in  the  flame 
itself.  In  the  blue-flame  stoves 
the  oil  is  vaporized  and  mixed 
with  air  before  it  reaches  the 
flame.  The  latter  type  is  prac- 
tically a  combined  gas  factory 
and  Bunsen  burner.  Figure  33 
shows  such  a  stove. 

Wood  alcohol  and  "  denatured  "  grain  alcohol  are  con- 
venient household  fuels  for  small  fires,  such  as  those  of 
chafing  dishes,  table  kettles,  and  coffee  percolators.  Wood 
alcohol  (methyl  alcohol)  is  a  product  of  the  destructive  dis- 
tillation of  wood  (see  Expt.  24,  p.  41),  and  therefore  a  by- 
product of  the  charcoal  industry.  Grain  alcohol  (ethyl 
alcohol)  is  produced  by  the  fermentation  of  sugars.  The 
reason  it  is  called  "  grain  "  alcohol  is  that  it  is  so  often  made 
by  converting  the  starch  of  grain,  such  as  corn  or  rye,  into 
sugar,  by  the  action  of  malt,  and  fermenting  the  sugar  so 
obtained.  But  it  is  also  made  from  molasses  and  from 
potatoes.  Ethyl  alcohol  is  the  active,  intoxicating  principle 
of  all  fermented  and  distilled  beverages.  Denatured  alcohol 
is  ethyl  alcohol  to  which  some  substance  has  been  added  to 
render  it  unpalatable.  Methylated  spirits  is  a  common 
variety  of  denatured  alcohol.  It  is  grain  alcohol  to  which  a 
small  proportion  (about  10  per  cent)  of  wood  alcohol  and 


FIG.  33.  —  A  blue  Jiame  kerosene 
stove. 


68  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

usually  a  small  proportion  of  some  other  substance,  such  as 
benzine,  has  been  added. 

Both  wood  alcohol  and  grain  alcohol  contain  the  three 
elements,  carbon,  hydrogen,  and  oxygen.  Both  liquids 
are  readily  ignited  and  burn  with  smokeless  flames. 

Three  quarts  of  grain  alcohol,  or  of  methylated  spirits, 
will  give  nearly  as  much  heat  as  four  quarts  of  wood  alcohol. 

The  present  importance  of  the  alcohols  as  fuels  is,  as 
already  stated,  a  secondary  one.  This  is  due  to  their  rela- 
tively high  price  as  compared  with  the  petroleum  products. 
The  quantity  of  these  two  alcohols  which  could  be  produced 
from  agricultural  products  is  practically  unlimited,  and  it  is 
possible  that  some  day  these  substances  may  find  more  use 
as  fuels  than  they  do  at  present. 

Gaseous  Fuels 

The  gases  most  used  in  the  household  for  fuel  purposes  are 
natural  gas,  coal  gas,  water  gas,  and  gasoline  or  "  air  "  gas. 

Natural  gas  exists  underground  in  certain  localities, 
usually  in  porous  strata,  whence  it  is  obtained  by  boring  wells. 
It  consists  of  the  compound  methane,  CH4,  mixed  with  small 
quantities  of  other  gases.  Used  with  suitable  burners  it 
is  the  most  convenient  and  most  efficient  of  all  the  natural 
fuels.  It  yields  about  1000  B.  T.  U.  per  cubic  foot.  Natural 
gas  is  supplied  to  many  of  the  cities  of  Pennsylvania,  Ohio, 
Indiana,  and  western  New  York.  In  Canada  it  occurs  in 
New  Brunswick,' Alberta,  and  other  places. 

Coal  gas,  made  by  the  destructive  distillation  of  bituminous 
coal,  constitutes  the  gas  supply  of  most  European  and  of 
many  American  cities.  The  coal  is  heated  in  closed  retorts, 
the  gases  produced  being  conducted  off  through  pipes. 
The  gases  are  purified  by  cooling,  washing  with  water,  and 
passing  through  lime  or  iron  oxide.  The  by-products  are 
gas  coke,  which  remains  in  the  retort;  coal  tar,  which  con- 


FUELS  69 

denses  from  the  gases  on  cooling,  and  from  which  numerous 
useful  compounds  are  manufactured  —  antiseptics  (such  as 
carbolic  acid),  dyes  (see  Chapter  XLIII),  etc.;  and  am- 
monia, which  remains  in  the  wash  water  (see  Chapter  XXIII). 
The  lime  and  iron  oxide  remove  the  sulphur  compounds  from 
the  gas. 

The  chief  constituents  of  coal  gas  are  free  hydrogen  and 
methane,  each  of  these  being  present  to  the  extent  of  about 


FIG.  34.  —  A  gas  stove. 

40  per  cent.  In  addition  to  these  two  main  constituents 
there  are  carbon  monoxide  (usually  6  to  8  per  cent)  and  some 
compounds  of  carbon  and  hydrogen,  other  than  methane. 
It  is  these  latter  hydrocarbons  which  make  the  gas  burn  with 
a  luminous  flame.  To  obtain  a  flame  which  will  not  deposit 
soot,  burners  on  the  principle  of  the  Bunsen  burner  are  used. 
In  such  burners  the  gas  is  mixed  with  air  before  ignition. 
Coal  gas  yields  600-625  B.  T.  U.  per  cubic  foot.  A  ton  of 
coal  yields  about  10,000  cubic  feet  of  gas,  which  contain 
only  about  one  fifth  of  the  original  fuel  value  of  the  ton  of 
coal. 

Water  gas  is  used  in  many  American  cities.  It  is  prepared 
by  passing  steam  through  white-hot  coke  or  anthracite  coal. 
The  chief  constituents  of  water  gas  are  carbon  monoxide  and 
hydrogen.  Gas  made  from  coke  contains  about  45  per 
cent  of  each  of  these  two  gases,  the  remaining  10  per  cent 
being  methane,  carbon  dioxide,  free  nitrogen,  and  free  oxygen. 


70  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Gas  made  from  anthracite  has  a  higher  proportion  of  these 
minor  constituents  —  about  20  per  cent  instead  of  10. 

Consisting  largely  of  carbon  monoxide,  water  gas  is 
extremely  poisonous  —  much  more  so  than  coal  gas.  The 
smallest  leakage  of  water  gas  from  pipes  or  cocks  is  therefore 
a  serious  matter.  Water  gas  has  from  40  to  60  per  cent  of  the 
fuel  value  of  the  coal  or  coke  from  which  it  is  made.  It 
yields  about  350  B.  T.  U.  per  cubic  foot,  but  the  fuel  value  is 
frequently  increased  by  enrichment.  (See  below.) 

Water  gas  burns  with  a  blue  flame,  which  has  very  low 
illuminating  power.  In  order  to  make  it  into  an  illuminating 
gas  for  use  with  old-style  burners,  it  is  common  to  mix  with 
it  a  gas  made  by  heating  petroleum  oils  to  a  high  temperature. 
(See  "Oil  gas,"  p.  77.)  This  process  is  called  enriching 
the  gas.  Enriched  water  gas  may  have  a  fuel  value  as  high 
as  700  B.  T.  U.  per  cubic  foot.  In  many  cities  a  mixture  of 
coal  gas  and  water  gas  is  used. 

Gasoline  gas  ("  air "  gas)  is  made  chiefly  in  private 
plants  for  the  supply  of  rural  homes  or  of  institutions  situated 
at  a  distance  from  a  city  supply.  It  is  a  mixture  of  gasoline 
vapor  and  air.  Gasoline  consists  of  the  more  volatile  hydro- 
carbons of  petroleum.  The  gas  is  made  from  it  by  exposing 
the  liquid  on  folds  of  canvas  to  a  current  of  air.  The  gasoline 
evaporates,  the  vapors  mixing  with  the  air,  the  supply  of 
which  is  so  regulated  that  the  hydrocarbons  will  not  become 
liquid  again  in  the  pipes.  The  gasoline  gas  burns  with  a 
luminous  (and  therefore  sooty)  flame,  but  a  blue  flame  is 
obtained  by  admitting  additional  air  at  the  burner,  which 
must  be  of  the  Bunsen  type. 

Compressed  and  Liquefied  Gas.  —  When  the  gas  mixtures 
used  for  fuel  purposes,  such  as  coal  gas  or  oil  gas,  are  subjected 
to  great  pressure,  some  of  the  constituents  (hydrocarbons 
containing  a  large  proportion  of  carbon)  liquefy.  This  liq- 
uefied portion  of  the  gas  may  be  separated  from  the  por- 
tion which  remains  in  the  gaseous  condition,  and  the  latter 


FUELS  71 

may  be  stored  in  cylinders  in  its  compressed  state  and  shipped 
to  houses  or  institutions  which  are  not  supplied  with  gas 
through  pipes. 

A  German  chemist,  named  Hermann  Blau,  has  patented 
a  process  in  which  some  of  the  constituents  of  oil  gas  are 
liquefied  and  removed,  then  the  remaining  gases  are  com- 
pressed to  a  liquid  condition.  Blau  gas  is  used  more  for 
lighting  than  for  cooking  purposes. 

Surface  Combustion 

Gas  burners  have  recently  been  designed  which  render  it 
possible  to  mix  the  gas  with  exactly  sufficient  air  for  its  com- 
plete combustion  and  to  cause  the  mixture  to  burn  flame- 
lessly  in  a  pile  of  granular  incombustible  material,  such  as 
pieces  of  silica,  SiO2,  or  alumina,  A^Os.  Combustion  of  gas 
so  conducted  is  termed  surface  combustion.  Surface  com- 
bustion is  very  economical  because  (i)  it  avoids  the  heating 
of  air  not  used  in  the  combustion,  and  (2)  heat  radiated  from 
the  incandescent  pile  of  refractory  material  is  more  penetra- 
tive than  heat  from  a  gas  flame.  It  is  claimed  that  surface 
combustion  gas  stoves,  doing  the  same  work  as  stoves  of 
the  ordinary  Bunsen  type,  will  use  35  to  45  per  cent  less  gas 
than  the  Bunsens. 

Further  information  on  liquid  and  gaseous  fuels,  including  numerous 
references  to  the  literature  of  the  subject,  will  be  found  in  Chapter  VT 
of  Benson's  "Industrial  Chemistry"  (New  York,  1913).  For  a  prac- 
tical method  of  comparing  the  values  of  the  common  household  fuels, 
the  reader  is  referred  to  Lynde's  "Physics  of  the  Household"  (New 
York,  1914),  pages  152-153. 


CHAPTER  XIII 

LIGHT  AND   ILLUMINANTS 

Experiment  36.* 

Materials : 

Platinum  wire,  2  or  3  inches. 

Iron  wire,  same  gauge  and  length. 

Magnesium  ribbon,  J  inch. 

Quicklime,  small  lump,  say,  J-inch  cube. 

Crucible  tongs  or  forceps. 

Blowpipe. 

(a)  With  the  tongs  hold  in  a  Bunsen  flame  side  by  side  a  piece 
of  iron  wire  and  a  piece  of  platinum  wire.     Note  the  gradual 
changes  of  color  as  the  temperature  of  the  wires  rises. 

(b)  Hold  a  piece  of  magnesium  wire  in  the  tongs,  and  ignite 
it  with  the  Bunsen  flame.     Note  the  white  light  emitted  as  the 
magnesium  burns.     (This  is  the  light  used  in  making  flashlight 
photographs.) 

The  ash,  which  remains  after  the  combustion  of  the  magnesium 
and  which  retains  something  of  the  form  of  the  original  ribbon,  is 
magnesium  oxide  (sometimes  called  magnesia).  Bring  this  ash 
again  into  the  flame  and  note  the  change  of  color  it  undergoes  as 
it  is  heated.  Blow  into  the  flame  with  the  blowpipe,  directing 
a  gentle  current  of  the  flowing  gases  towards  the  magnesia.  Does 
it  become  brighter?  Is  its  color  altered?  (c)  Hold  a  piece  of 
lime  in  the  flame  a  little  above  the  inner  cone.  Note  its  color. 
Blow  the  flame  upon  it  with  the  blowpipe.  Does  the  color  change  ? 
If  an  oxy hydrogen  blowpipe  is  available,  direct  its  flame  against 
the  lime.  Is  more  light  now  emitted  ?  What  is  its  color  ? 

When  substances  are  heated  to  a  sufficiently  high  tem- 
perature, they  give  out  light.  They  are  then  said  to  be  in  an 
incandescent  condition.  Like  heat,  light  is  a  form  of  energy, 
and  incandescence  is  due  to  a  transformation  of  some  of  the 
heat  into  light. 

72 


LIGHT  AND   ILLUMINANTS 


73 


Gases  can  be  heated  to  incandescence,  and  the  colors  of 
the  light  they  then  give  out  are  characteristic  of  the  various 
substances.      Each  gaseous  compound  yields  its  own  color, 
unless  when  heated  to  in- 
candescence   it    is    decom- 
posed,   in    which    event   it 
gives  the  colors  of  its  decom- 
position products. 

To  obtain  the  characteristic  colors  of  gases,  a  glass  tube 
provided  with  metal  electrodes  (see  Fig.  35)  is  first  filled  with 
the  gas.  Then  most  of  the  gas  is  pumped  out  and  the  tube 
is  sealed  by  melting  the  glass.  On  passing  the  electric  dis- 
charge (spark)  from  an  induction  coil  through  the  gas  from 


FIG.  35.  —  A  form  of  tube  in  which  gases 
are  electrically  heated  to  incandescence. 


FIG.  36.  —  Bunsen  and  Kirchhoff's  Spectroscope. 
used  in  the  analysis  of  light. 


An  instrument 


electrode  to  electrode  the  characteristic  light  appears.  The 
color  of  the  light  may  be  analyzed  by  means  of  an  instrument 
called  a  spectroscope. 

It  was  by  the  color  of  its  light  that  the  element  helium  was 


74  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

discovered  in  the  sun's  atmosphere  many  years  before  it  wa 
found  upon  our  planet ;  and  it  was  from  observations  of  ligh 
color  that  astronomers  inferred  that  the  tail  of  Halley's  come 
(visible  in  1910)  contained  cyanogen  gas  (C2N2).  Incan 
descent  sodium  vapor  emits  yellow  light ;  potassium,  violet 
calcium,  red;  barium  and  copper,  green,  etc.;  and  most  com 
pounds  of  these  metals  when  heated  in  a  Bunsen  flame  impar 
to  it  these  characteristic  colors: 

Experiment  37.* 

Materials : 

Small  portions  of  the  chlorides  of  sodium,  potassium,  calcium 

strontium,  and  barium. 
Platinum  wires  sealed  in  glass  handles  and  carefully  cleanec 
by  alternate  heating  in  Bunsen  flame  and  dipping  in  pure 
concentrated  hydrochloric  acid  until  they  do  not  color  the 
flame. 

Heat  a  clean  platinum  wire  and  dip  it  while  hot  into  one  of  the 
salts,  then  bring  again  into  the  Bunsen  flame  and  note  the  color 
imparted  to  it.  Repeat  with  the  other  salts,  using  a  thoroughly 
clean  wire  in  each  instance. 

In  practical  illumination,  however,  the  incandescence  o 
solids  is  of  much  more  importance  than  that  of  gases.  The 
color  of  the  light  emitted  by  an  incandescent  solid  depends 
not  only  on  what  substance  the  solid  is,  but  also  on  the  tem- 
perature to  which  it  is  heated.  As  the  temperature  of  any 
solid  is  gradually  raised,  red  light  is  first  emitted,  then  the 
other  colors  of  the  rainbow  are  successively  combined  with  the 
red  until  finally  white  light  (which  is  composed  of  all  the  rain- 
bow colors)  is  given  out.  The  terms  commonly  used  to  dis- 
tinguish high  temperatures  are  said  to  correspond  roughly  to 
the  following  points  on  the  Centigrade  and  Fahrenheit  scales 

Incipient  red  heat     .     .     .     .     .     .  525°  C.  or  1000°  F. 

Dull  red  heat        700°  C.  or  1300°  F. 

Bright  red  heat     .......  950°  C.  or  1750°  F. 

Yellow  heat ,    .  1100°  C.  or  2000°  F. 

White  heat       1500°  C.  or  2700°  F. 


LIGHT  AND   ILLUMINANTS  7$ 

Substances  which  radiate  heat  badly  are  more  readily  heated 
to  high  temperatures  than  good  heat  radiators.  This  fact 
is  taken  advantage  of  in  "  gas  mantle  "  lighting  (see  p.  78). 

Experiment  38. 

Materials : 
Candle. 

Kerosene  lamp. 

Porcelain  dish  or  piece  of  broken  porcelain. 
Hold  a  cold  piece  of  porcelain  in  the  flame  of  (i)  a  candle,  (2)  a 
kerosene  lamp,  (3)  a  luminous  gas  flame. 


Candles  and  Lamps 

In  the  more  primitive  methods  of  lighting  —  the  candle, 
the  gas  light,  and  the  oil  lamp  —  the  light  is  given  off  by 
the  particles  of  carbon  which  are  formed  by  the  decomposi- 
tion of  some  of  the  hydrocarbon  gases  of  the  flame.  For  the 
heat  of  the  flame  not  only  changes  the  liquid  oil  or  the  solid 
candle  into  gases,  but  decomposes  these  gases  into  simpler 
constituents,  one  of  which  is  carbon.  Lampblack  is  manu- 
factured by  cooling  the  luminous  flame  of  pine  knots,  crude 
petroleum,  or  natural  gas,  by  means  of  a  metal  plate  or  re- 
volving drum,  or  by  burning  such  substances  in  a  limited 
draft  of  air  and  conducting  the  smoke  into  settling  cham- 
bers. Where  such  flames  are  used  for  lighting  purposes  the 
supply  of  air  must  be  sufficient  to  cause  the  carbon  to  burn 
completely  in  the  outer  layers  of  the  flame.  One  great  ad- 
vantage of  a  lamp  over  an  open  flame  is  that  the  chimney 
promotes  an  upward  draft  of  air  around  the  flame  and  thus 
permits  the  fuel  to  be  supplied  to  the  flame  at  a  rate  which 
would  cause  smoking  in  an  open  flame.  As  air  is  supplied 
more  rapidly  to  the  flame  the  fuel  gases  can  also  be  more 
rapidly  supplied.  The  result  is  a  brighter,  more  intense 
light.  It  is  possible,  however,  as  every  one  knows,  to  supply 
fuel  too  rapidly  to  a  lamp  flame  —  by  turning  up  too  much 


76  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

of  the  wick.  This  causes  smoking  in  the  lamp,  with  conse- 
quent deposition  of  soot  on  the  chimney. 

Candles  were  formerly  made  of  tallow.  The  materials 
now  commonly  used  for  the  cheaper  kinds  of  candles  are  (i) 
paraffin  and  (2)  a  mixture  of  solid  acids  made  from  animal 
or  vegetable  fats  and  known  commercially  as  • "  stearin" 
Wax  and  spermaceti  candles  are  more  expensive.  The  wax 
most  used  is  beeswax  bleached  by  sunlight ;  spermaceti  is  a 
wax  obtained  from  the  sperm  whale.  Mixtures  of  these 
various  materials  are  sometimes  used,  —  spermaceti  and 
stearin,  etc. 

The  earliest  lamps  burned  vegetable  and  animal  fatty  oils, 
such  as  olive  oil,  lard  oil,  and  whale  oil.  Lamps  for  petroleum 
oils  were  first  made  about  1853,  and  after  the  discovery  of 
petroleum  in  Pennsylvania  (1859)  they  quickly  replaced  the 
older  forms.  To-day  kerosene  is  the  universal  lamp  fuel  in 
America.  Its  one  disadvantage,  as  compared  with  the  fatty 
oils  previously  used,  lies  in  the  possibility  of  explosions. 
Much  ingenuity  has  been  expended  upon  the  construction 
of  lamps,  and  the  best  types  now  on  the  market  can  be 
used  with  little  risk,  provided  they  are  kept  in  good  con- 
dition. Explosions  can  only  occur  when  the  bowl  of  the 
lamp  contains  a  mixture  of  oil  vapor  and  air  in  explosive 
proportions,  and  when  that  mixture  is  ignited.  Ignition  of 
the  mixture  may  occur  either  through  the  wick  being  turned 
down  so  far  that  the  lighted  portion  comes  in  contact  with 
the  gas  in  the  bowl,  or  through  a  portion  of  the  explosive 
mixture  reaching  the  flame,  or  vice  versa. 

The  danger  of  explosion  may  be  lessened  by  (i)  keeping 
the  lamp  clean  —  free  from  charred  wick,  oil,  and  dirt  of 
all  kinds ;  (2)  keeping  the  bowl  well  filled,  so  as  to  lessen  the 
space  available  for  the  accumulation  of  explosive  gas;  (3) 
using  only  a  loosely  plaited,  soft,  long-staple  cotton  wick, 
and  soaking  it  in  oil  before  lighting  it  the  first  time;  (4)  avoid- 
ing moving  the  lamp,  and  (in  case  it  must  be  moved)  carrying 


LIGHT  AND   ILLUMINANTS  77 

it  steadily  so  as  not  to  shake  up  the  oil ;  (5)  putting  out  the 
light  by  means  of  an  extinguisher,  or,  if  the  lamp  be  not  pro- 
vided with  one,  turning  down  the  wick  until  the  flame  flickers, 
and  then  blowing  a  sharp  puff  of  breath  across  the  top  of  the 
chimney,  but  not  down  it. 

Lamps  with  side  fillers  should  not  be  purchased.  If  they 
are  in  use,  the  side  fillers  should  be  kept  well  closed.  Of 
course,  oil  should  never  be  poured  into  the  bowl  of  a  lighted 
lamp.  Lamps  with  the  wick  tube  well  extended  down  into 
the  bowl,  or  prolonged  into  a  wire-gauze  wick  mantle,  are 
safer  than  those  without  such  an  appliance.  Lamps  with 
metal  bowls  are  much  safer  than  those  with  glass  bowls. 
It  is  only  rarely  that  a  glass  bowl  is  shattered  by  an  explosion, 
but  the  alarm  caused  by  the  explosion  is  apt  to  result  in  the 
lamp  being  dropped,  in  which  case  the  glass  bowl  is  apt  to 
be  broken  and  the  oil  ignited.  Wicks  should  be  long  enough 
to  trail  on  the  bottom  of  the  bowl  for  about  two  inches. 
When  this  two  inches  is  burned  off,  the  wick  should  be 
renewed. 

Gas  Lights 

The  older  methods  of  gas  lighting  depend  on  the  same 
principle  as  the  candle  and  kerosene  lights.  Carbon  is 
liberated  within  the  flame  and  heated  to  incandescence. 
The  amount  of  light  obtained  depends  on  (i)  the  number  of 
carbon  particles  liberated  and  (2)  the  temperature  to  which 
they  are  heated.  Coal  gas  and  gasoline  gas  (see  p.  70)  con- 
tain sufficient  of  the  so-called  higher  hydrocarbons  —  those 
containing  a  higher  proportion  of  carbon  than  does  methane 
-  to  give  luminous  flames.  So  also  do  "  oil  "  gas  and  acety- 
lene gas. 

Oil  gas  is  made  from  certain  heavy  oils ;  for  instance,  some 
of  the  heavier  petroleum  products.  The  oils  are  vaporized 
by  heating  and  the  vapors  then  subjected  to  a  still  higher 
temperature  (1800°  F.).  The  heavy  molecules  of  the  oils 


78  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

are  thus  decomposed  into  the  smaller  molecules  of  substances 
which  remain  gaseous  at  ordinary  temperatures.  The  pro- 
cess is  known  technically  as  "  cracking."  Oil  gas  is  often 
compressed  into  cylinders  for  transportation.  It  has  been 
and  is  still  much  used  for  lighting  railway  cars.  It  requires 
a  special  form  of  burner. 

Acetylene  gas  differs  from  other  illuminating  gases  in 
consisting,  not  of  a  mixture,  but  of  a  single  chemical  com- 
pound, C2H2.  It  is  formed  by  the  action  of  water  on  calcium 
carbide,  CaC2,  a  substance  made  in  the  electric  furnace  from 
lime  and  coke.  The  reaction  occurring  in  an  acetylene  gener- 
ator is  the  following : 

CaC2  +  2  H2O  =  Ca  (OH)2  +  C2H2 

Calcium  carbide  +  Water     =     Slaked  lime    +  Acetylene 

It  requires  a  special  form  of  burner,  but  gives  a  brilliant 
white  light.  Its  great  disadvantage  is  its  explosiveness. 
Not  only  does  it  form  explosive  mixtures  with  air,  but  in  a 
compressed  state  it  is  itself  explosive.  Although  acetylene 
was  at  first  used  exclusively  for  lighting  purposes,  it  is  now 
used  also  for  cooking  and  heating. 

Natural  gas  and  water  gas  do  not  burn  with  sufficiently 
luminous  flames  for  illuminating  purposes.  They  are,  how- 
ever, rendered  suitable  for  such  purposes  by  adding  to  them 
a  suitable  quantity  of  the  "  higher  hydrocarbons."  This 
may  be  added  in  the  form  of  light  petroleum  oils,  such  as 
benzine,  or  in  the  form  of  oil  gas.  (See  p.  70.) 

Gas  Mantles 

Another  device  much  used  to  obtain  light  from  flames 
which  otherwise  are  non-luminous  is  to  suspend  in  them  an 
incombustible  solid  capable  of  converting  a  part  of  the  heat 
of  the  flame  into  light.  The  first  substance  used  success- 
fully for  this  purpdse  was  lime.  To  obtain  light  from  lime 
a  very  high  temperature  is  necessary,  as  the  light  obtained 


LIGHT  AND   ILLUMINANTS  79 

is  white.  A  small  quantity  of  fine  lime  powder  can  be 
heated  to  the  requisite  temperature  by  the  heat  of  an  alcohol 
burner  (spirit  lamp).  To  heat  a  large  pencil  of  lime,  how- 
ever, it  is  necessary  to  supply  undiluted  oxygen  to  a  flame 
of  hydrogen  or  of  one  of  the  commercial  illuminating  gases. 
The  oxyhydrogen  limelight  has  been  much  used  in  pro- 
jecting lanterns,  and  we  owe  the  familiar  phrase  "  to  stand 
in  the  limelight  "  to  the  use  of  such  lanterns  in  the  theater. 
At  the  present  time  the  limelight  has  been  largely  super- 
seded for  such  purposes  by  the  electric  arc  light. 

The  success  of  the  limelight  prompted  many  attempts 
to  find  other  incombustible  and  infusible  substances  which 
could  be  used  to  convert  some  of  the  heat  of  non-luminous 
flames  into  light.  The  "  mantle  "  invented  by  Auer  von 
Welsbach  represents  the  result  of  the  most  successful  of  these 
attempts.  This  mantle  consists  of  a  mixture  of  the  oxides 
of  two  of  the  rarer  metals  —  thorium  and  cerium.  The  mix- 
ture which  gives  the  best  results  is  composed  of  i  part  of 
cerium  oxide  to  99  parts  of  thorium  oxide.  A  fabric  of  ramie 
or  mercerized  cotton  is  made  into  the  form  of  the  desired 
mantle,  and  is  sewed  with  asbestos  thread.  This  mantle 
of  textile  fabric  is  then  soaked jn  a  solution  of  the  nitrates 
of  the  metals.  When  the  mantle  is  "  burned  off,"  the  or- 
ganic matter  is  oxidized  and  passes  off.  At  the  same  time 
the  nitrates  are  decomposed,  yielding  gases  (which  pass  off) 
and  the  oxides,  which  remain  as  an  ash,  retaining  the  form 
of  the  original  fabric.  The  flame  used  to  heat  these  mantles 
is  a  Bunsen  flame.  For  the  same  amount  of  gas  burned 
these  incandescent  burners  give  6  to  8  times  as  much  light 
as  the  best  of  the  old  flat-flame  burners,  and  5  to  6  times 
as  much  light  as  the  round  flame  (Argand)  burners,  which 
depended  for  their  luminosity  on  the  incandescence  of  lib- 
erated carbon. 


8o  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Electric  Lighting 

There  are  two  processes  of  electric  lighting,  viz.  the  arc 
and  the  incandescent  electric  light.  As  the  former  is  used 
only  for  lighting  streets  and  large  buildings  it  need  not  be 
considered  here. 

In  the  most  common  forms  of  incandescent  electric  light 
a  filament  of  carbon  or  a  wire  of  some  metal,  such  as  tungsten 
or  tantalum,  is  heated  to  incandescence  by  means  of  an  elec- 
tric current.  As  the  filament  or  wire  is  enclosed  in  a  glass 
bulb  from  which  the  air  has  been  pumped  out,  no  combustion 
occurs.  The  light  and  heat  produced  come  directly  from  the 
electric  energy  of 'the  current.  Incandescent  electric  lights, 
therefore,  neither  use  up  the  oxygen  of  the  house  air  nor  give 
off  any  products  of  combustion  nor  any  leakage  products 
to  contaminate  the  air. 

Electric  lights  are  more  conveniently  lighted  and  extin- 
guished, and  are  less  dangerous  than  any  of  the  other  forms 
of  light.  They  require  less  attention  than  incandescent  gas 
lights  and  much  less  than  lamps  or  candles. 

Filament  lamps,  particularly  those  of  carbon,  deteriorate 
in  use.  Some  of  the  material  of  the  filament  vaporizes  and 
condenses  on  the  inner  surface  of  the  glass.  This  both  dark- 
ens the  glass  and  weakens  the  filament.  The  "  burning- 
out  "  of  lamps  is  due  to  the  breaking  of  the  filament.  It  is 
usually  economical  to  discard  a  lamp  before  the  filament 
becomes  thin  enough  to  break,  because,  as  the  filament  de- 
teriorates, the  light-giving  power  of  the  lamp  is  greatly  di- 
minished. When  the  light  becomes  reddish  in  color,  the 
lamp  should  be  replaced  by  a  new  one. 

The  metallic  filament  lamps  commonly  made  at  the  present 
time  use  only  about  one  third  the  current  used  by  carbon 
lamps  of  the  same  candle  power,  that  is  to  say,  of  the  same 
light-giving  power.  The  earlier  tungsten  filaments  were 
very  fragile,  and  the  lamps  had  to  be  handled  much  more 


LIGHT  AND   ILLUMINANTS  8 1 

carefully  than  carbon  lamps.  But  means  have  been  found 
of  making  stronger  tungsten  filaments,  and  the  best  modern 
ones  are  sufficiently  strong  for  most  purposes.  Metallic 
filaments  are  stronger  when  hot  than  when  cold.  In  dusting 
or  cleaning  lamps  of  this  type  the  current  should  be  turned 
on  during  the  operation. 

Carbon  filaments  and  tungsten  filaments  last  about  the 
same  length  of  time.  They  average  about  1000  hours  of 
actual  lighting,  or  about  one  year's  ordinary  household 

service. 

i 

For  discussion  of  the  physical  properties  of  light  with  special  reference 
to  the  household  the  reader  is  referred  to  pages  246-273  of  Lynde's 
"  Physics  of  the  Household"  (New  York,  1914). 


CHAPTER  XIV 
ACIDS   AND    SALTS 

THE  following  experiments  are  designed  to  show  what 
common  characteristics  the  substances  called  acids  have, 
and  to  illustrate  the  relations  existing  among  acids,  metals, 
and  the  substances  called  salts. 

Experiment  39. 

Materials  : 

Tartaric  acid,  a  few  crystals. 

Citric  acid,  a  few  crystals. 

Magnesium  ribbon,  6  or  8  pieces,  ^  inch  long. 

Copper  foil,  2  pieces,  \  inch  X  \  inch. 

Zinc  foil,  half  a  dozen  pieces,  i  inch  X  \  inch. 

1.  Label  six  test  tubes  and  fill  them  with  distilled  water.    Into 
them  put  respectively: 

(1)  One  or  two  drops  concentrated  sulphuric  acid. 

(2)  One  or  two  drops  concentrated  hydrochloric  acid. 

(3)  Five  to  ten  drops  reagent  acetic  acid. 

(4)  A  few  crystals  tartaric  acid. 

(5)  A  few  crystals  citric  acid. 

(6)  Nothing. 

2.  Shake  each  tube  to  mix  the  contents.     Use  them  for  the 
following  experiments : 

(a)  Taste  each.     What  similarity  of  taste  do  you  observe  in 
the  tubes  to  which  acid  was  added  ? 

(b)  Test  each  with  blue  litmus  paper. 

(c)  Pour  out  a  small  portion  of  each  into  another  test  tube  and 
add  a  piece  of  magnesium  ribbon.     Describe  and   explain  what 
occurs.    What   three  characteristics  are  common  to  the  acids 
tested  ? 

Experiment  40. 

Materials  " 

Acid  solutions  prepared  for  Experiment  39. 
Copper  foil,  2  pieces,  ^  inch  X  i  inch. 
82 


ACIDS  AND   SALTS  83 

Zinc  foil,  4  pieces,  i  inch  X  \  inch. 
Iron  fillings. 

To  what  class  of  elements  do  the  four  substances,  magnesium, 
zinc,  iron,  and  copper,  of  which  you  have  specimens,  belong? 
What  properties  are  common  to  the  four  ? 

To  discover  whether  zinc  and  iron  are  acted  upon  by  acids  as 
the  magnesium  was,  place  two  portions  of  each  in  separate  test 
tubes  and  add  a  little  of  any  two  of  the  acid  solutions  prepared 
for  Experiment  39. 

Test  copper  in  the  same  way.  Also  heat  concentrated  hydro- 
chloric acid  till  it  just  begins  to  boil,  remove  from  flame,  and  when 
boiling  ceases,  add  a  piece  of  copper  foil. 

From  your  experiments  infer  whether  every  acid  acts  on  every 
metal. 

Experiment  41. 

Materials : 

Magnesium  ribbon  in  pieces  of  about  0.25  gram. 

Zinc  foil,  i  inch  X  |  inch. 

To  discover  what  products  are  formed  by  the  action  of  acids 
on  metals  make  the  following  experiments  : 

(a)  Place  a  piece  of  magnesium  ribbon  in  a  test  tube  and  pour 
in  enough  dilute  sulphuric  acid  to  cover  it.     Keep  the  mouth  of 
the  tube  covered  with  the  thumb  for  a  minute  or  two ;  then,  bring- 
ing the  flame  of  a  burner  or  match  to  the  mouth  of  the  tube, 
remove  the  thumb.     If  no  effect  is  noted,  keep  the  tube  closed 
for  a  longer  time  and  then  apply  the  flame  again.     Add  a  little 
more  magnesium  and  set  the  tube  aside  for  Experiment  (d). 

(b)  Treat  magnesium  with  dilute  hydrochloric  acid,  testing  the 
gas  evolved  as  in  (a) . 

(c)  Treat  zinc  with  dilute  sulphuric  or  dilute  hydrochloric  acid 
and  test  the  gas  evolved  as  in  (a). 

(d)  Filter  off  any  magnesium  left  undissolved  in  (<z),  collecting 
the  filtrate  (liquid  which  runs  through  the  filter)  in  a  dish.     Evap- 
orate this  filtrate   to  dryness    under  the    hood.     Examine  what 
remains  in  the  dish. 

What  gas  is  produced  by  the  action  of  an  acid  on  a  metal  ?  Is 
this  gas  an  element?  From  which  of  the  reagents  (substances 
entering  into  the  chemical  change)  is  this  gas  derived?  Can  it 
be  from  the  metal?  From  the  water?  Recall  experiment  with 
magnesium  and  water  without  acid.  What  element  is  common  to 
all  acids? 


84  ELEMENTARY   HOUSEHOLD   CHEMISTRY 

Experiment  42.* 

Materials : 

Sodium  in  small  pieces  under  oil. 
Alcohol. 
Ether. 
Apparatus : 

Forceps  to  handle  the  sodium. 
Filter  paper. 

(Where  this  experiment  is  made  for  demonstration  purposes 
the  use  of  a  filter  pump  is  recommended.) 

In  an  evaporating  dish  under  the  hood  place  a  little  concentrated 
hydrochloric  acid.  Cut  sodium  into  pieces  smaller  than  a  pea, 
dry  them  with  filter  paper,  and  add  one  by  one  to  the  hydrochlo- 
ric acid.  What  gas  is  given  off?  (See  Expt.  41.)  Note  what 
forms  in  the  acid.  Filter,  wash  with  alcohol,  then  with  ether, 
allow  to  dry,  and  taste.  What  familiar  substance  is  the  product 
of  the  action  of  hydrochloric  acid  on  sodium?  This  substance 
lends  its  name  to  the  class  of  solid  substances  produced  by  the 
interaction  of  metals  and  acids. 

There  is  a  large  class  of  compounds  of  hydrogen  having 
the  following  characteristics  in  common : 

(1)  They  taste  sour. 

(2)  Their  aqueous  solutions  turn  blue  litmus1  red. 

(3)  They  react  with  many  metals,  setting  hydrogen  free. 

Compounds  of  this  class  are  known  as  acids.  A  few  of 
the  acids  contain  only  one  other  element  combined  with  their 
hydrogen.  Thus,  hydrochloric  acid  (called  also  muriatic 
acid)  is  simply  hydrogen  chloride,  HC1;  and  hydrofluoric 
acid,  simply  hydrogen  fluoride,  HF. 

The  majority  contain  some  oxygen.  Thus,  sulphuric 
acid,  H2SO4,  contains  hydrogen,  sulphur,  and  oxygen ;  nitric 
acid,  HNO3,  contains  hydrogen,  nitrogen,  and  oxygen.  The 
organic  acids,  of  which  there  are  a  great  many,  always  con- 
tain carbon,  hydrogen,  and  oxygen.  The  sour  taste  of  fruits 

1  Litmus  is  a  coloring  matter  derived  from  lichens  found  on  trees  and  cliffs 
on  the'  sea  coasts  of  Europe. 


ACIDS   AND   SALTS  85 

is  due  to  organic  acids.  The  chief  acid  of  grapes  is  tartaric, 
H2C4H4O6 ;  of  apples,  pears,  and  mountain  ash  berries,  malic, 
H2C4H4O5;  of  lemons,  oranges,  gooseberries,  cranberries, 
and  currants,  citric,  H3C6H5O7.  Vinegar  owes  its  sourness 
to  acetic  acid,  JiC^H-sOz-  Sour  milk  contains  lactic  acid, 
HCsH^Os,  and  rancid  butter,  butyric  acid,  HC4H7O2. 

Salts 

Whenever  an  acid  acts  upon  a  metal,  not  only  is  hydrogen 
set  free,  but  there  is  produced  also  a  compound  belonging  to 
the  class  known  as  salts.  In  the  majority  of  cases,  if  water  is 
present,  the  salt  is  left  in  solution  in  the  water.  Thus : 

Sodium  with  hydrochloric  acid  yields  hydrogen  and  com- 
mon salt  (sodium  chloride). 

Zinc  with  sulphuric  acid  yield  hydrogen  and  zinc  sul- 
phate. 

Magnesium  with  acetic  acid  yields  hydrogen  and  mag- 
nesium acetate. 

In  general  terms,  then,  we  may  write : 

Metal  +  Acid  =  Salt  +  Hydrogen 

The  salt  is  composed  of  the  metal  and  the  elements  of  the 
acid  other  than  the  hydrogen  set  free. 

Thus,  common  salt  is  a  compound  of  sodium  with  the 
chlorine  of  the  hydrochloric  acid ;  zinc  sulphate,  a  compound 
of  zinc  with  the  sulphur  and  oxygen  of  the  sulphuric  acid; 
and  magnesium  acetate  a  compound  of  magnesium  with  the 
carbon,  oxygen,  and  three  fourths  of  the  hydrogen  of  acetic 
acid. 

This  may  perhaps  be  made  clearer  by  writing  the  equations 
for  the  above  reactions : 

Metal  +      Acid  Salt  +  Hydrogen 

2Na  +  2HC1  =  2NaCl                +          H2 

Zn  +        H2SO4  =  ZnSO4  +          H2 

Mg  +        H2SO4  =  MgSO4  +          H2 

Mg  +  2  HC2H302  =  Mg  (C2H302)2  +          H2 


86  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Acid   Radicles 

The  common  constituent  of  the  acid  and  salt  —  the  Cl,  the 
SO4,  and  the  C2H3O2  —  is  known  as  the  acid  radicle.1  It  does 
not  exist  as  a  separate  substance,  but  is  present  in  the  acid 
and  all  its  salts.  Thus,  the  acid  may  be  regarded  as  a  com- 
pound of  the  radicle  with  hydrogen,  and  the  salts  as  com- 
pounds of  the  radicle  with  metals.  The  formulas  of  radicles 
customarily  include  one  or  more  dashes  representing  the 
bonds  that  join  the  radicles  to  the  hydrogen  or  metal.  Thus : 

— Cl,     =S04,    — ( 


Definitions  of  Acid  and  Salt 

An  acid  may  be  defined  as  a  substance  containing  hydrogen, 
replaceable  by  a  metal,  and  a  salt  as  a  compound  derived  from 
an  acid  by  the  replacement  of  hydrogen  by  a  metal. 

Nomenclature  of  Salts    . 

It  will  be  noted  that,  as  a  rule,  the  name  of  the  salt  is 
obtained  from  that  of  the  acid  by  substituting  the  suffix  -ate 
for  the  suffix  -ic.  Thus,  the  salts  of  nitric  acid  are  nitrates, 
those  of  acetic  acid,  acetates,  etc.  An  important  exception  is 
hydrochloric  acid,  whose  salts,  being  compounds  of  metals 
and  chlorine,  are  called  chlorides.  Thus,  NaCl,  Sodium 
chloride ;  FeCla,  Iron  chloride ;  etc.  --\^ 

Notation 

The  formulas  of  acids  and  salts  are  always  so  written  as 
to  indicate  clearly  what  acid  radicle  they  contain.  For 
example,  the  formulas  of  all  nitrates  have  the  nitrate  radical, 
We  therefore  write  the  formula  of  calcium  nitrate 

1  Also  spelled  radical. 


ACIDS  AND   SALTS  87 

Ca(NO3)2,  rather  than  CaN2O6  ;  and  that  of  aluminium  sul- 
phate A12  (SOOs,  rather  than  Al2S3Oi2.  For  the  same  reason, 
in  writing  the  formulas  of  the  organic  acids,  the  replaceable 
hydrogen  atoms  are  written  separately  from  the  hydrogen 
atoms  which  form  a  part  of  the  radicles.  Thus,  tartaric  acid, 
not  H6C4O6;  and  acetic  acid,  HC2H3O2,  not 


Valence 

When  sodium  or  potassium  or  silver  replaces  the  hydrogen 
of  an  acid,  one  atom  of  the  metal  is  regarded  as  having  re- 
placed each  atom  of  hydrogen  driven  out  of  the  molecule. 
Thus  nitric  acid,  HNO3,  yields  the  salts  NaNO3,  KN03,  and 
AgNO3;  sulphuric  acid,  H2SO4,  the  salts  Na2SO4,  K2SO4,  and 
Ag2S04;  and  phosphoric  acid,  H3PO4,  the  salts  Na3PO4, 
K3PO4,  and  Ag3PO4.  But  the  magnesium  and  calcium  atoms 
are  regarded  as  having  each  the  power  of  replacing  two 
atoms  of  hydrogen.  We  have  therefore  for  the  nitrates  of 
these  metals  the  formulas  Mg(NO3)2  and  Ca(NO3)2  ;  for  the 
sulphates  MgSO4  and  CaSO4;  and  for  the  phosphates 
Mg3(PO4)2  and  Ca3(PO4)2.  In  the  magnesium  nitrate  the 
atom  of  magnesium  has  replaced  the  hydrogen  atoms  in 
two  molecules  of  the  acid  ;  in  the  sulphate  it  has  replaced 
the  two  atoms  of  the  sulphuric  acid  molecule,  H2SO4  ;  in  the 
phosphate  three  atoms  of  magnesium  have  replaced  the  six 
atoms  of  hydrogen  in  two  molecules  of  phosphoric  acid. 

The  aluminium  atom  replaces  three  atoms  of  hydrogen. 
The  formulas  of  aluminium  nitrate,  sulphate,  and  phosphate 
are,  therefore,  A1(NO3)3,  A12(SO4)3,  and  A1PO4. 

The  valence  of  a  metal  is  the  number  of  atoms  of  hydrogen 
which  its  atom  will  replace. 

Thus,  sodium,  potassium,  and  silver  have  a  valence  of  one. 
These  metals  are  said  to  be  univalent. 

Magnesium  and  calcium  have  a  valence  of  two.  They  are, 
therefore,  called  bivalent  metals. 


88  ELEMENTARY  HOUSEHOLD    CHEMISTRY 

Aluminium  has  a  valence  of  three.     It  is  trivalent. 

Some  metals  have  one  valence  in  one  set  of  compounds  and 
another  valence  in  another  set.  Thus,  iron  in  ferrous  oxide, 
FeO,  ferrous  chloride,  FeCl2,  and  ferrous  sulphate,  FeSO4, 
is  bivalent ;  but  in  ferric  oxide,  Fe2O3,  ferric  chloride,  FeCl3, 
and  ferric  sulphate,  Fe2(SO4)3,  it  is  trivalent.  Mercury  in 
mercurous  chloride  (calomel),  HgCl,  is  univalent;  in  mer- 
curic chloride  (corrosive  sublimate),  HgCl2,  it  is  bivalent. 

The  term  valence  is  also  used  with  reference  to  the  non- 
metallic  elements.  Thus  oxygen  is  said  to  be  bivalent  because 
its  atom  combines  with  two  atoms  of  hydrogen,  forming 
H2O;  and  chlorine  is  univalent  in  many  of  its  compounds, 
such  as  HC1  and  its  salts,  KC1,  NaCl,  CaCl2,  etc. 

The  acid  radicles,  — Cl,  — NOs,  and  — C2H3O2,  may  also 
be  said  to  be  univalent ;  =  SC>4,  =  COs,  =  C2C>4,  etc.  to  be 
bivalent;  and  =  PC>4,  to  be  trivalent. 

Acid  Salts 

Acids  whose  molecules  have  more  than  one  atom  of  re- 
placeable hydrogen  may  form  compounds  in  which  only  a 
part  of  the  replaceable  hydrogen  is  actually  replaced  by  a 
metal.  Thus  if  half  the  hydrogen  of  sulphuric  acid  is  re- 
placed by  sodium,  we  have  NaHSO4 ;  when  one  third  of  the 
hydrogen  of  phosphoric  acid  is  replaced  by  potassium,  we  have 
KH2PC>4 ;  and  when  two  thirds  of  the  hydrogen  of  phosphoric 
acid  is  replaced  by  potassium,  we  have  K2HP(>4. 

These  compounds  come  within  our  definition  of  salts  be- 
cause they  are  formed  from  acids  by  replacement  of  hydro- 
gen by  metals.  But  they  also  come  within  our  definition  of 
acids  because  they  contain  hydrogen  replaceable  by  metals. 
They  are  therefore  called  acid  salts.  Among  the  important 
acid  salts  we  have : 

Acid  sodium  carbonate,  more  commonly  called  sodium 
bicarbonate,  or  baking  soda,  NaHCOa. 

Acid  sodium  sulphate  or  sodium  bisulphate,  NaHSO4. 


ACIDS    AND   SALTS  89 

Acid  potassium  sulphate  or  potassium  bisulphate,  KHSO4. 

Acid  potassium  oxalate,  potassium  binoxalate,  "  salt  of 
sorrel  "  or  "  salt  of  lemons,"  KHC2O4. 

Acid  potassium  tartrate,  potassium  bitartrate  or  "  cream 
of  tartar,"  KHC^Oe. 

Disodium  phosphate,  Na2HPO4.  This  is  the  most  common 
phosphate  of  sodium  and  is  often  called  simply  sodium  phos- 
phate. 

Monocalcium phosphate,  acid  phosphate  of  lime,  Ca(H2PO4)2 
or  CaH4(PO4)2. 

EXERCISES 

1.  Write  the  formulas  and  names  of  the  acids  corresponding 
to  the  salts  whose  formulas  follow: 

(i)NaN03          (2)KN02  (3)  MgSO3  (4)  MgS04 

(5)  HgCl2  (6)  HgCl  (7)  FeCl2  (8)  FeCl3 

(9)  AgCl  (10)  Ag2S04          (n)  A12(S04)3         (12)  A1P04 

2.  Give  the  valences  of  the  metals  in  Exercise  i. 

3.  Write  the  names  of : 

(1)  The  sodium  salt  of  nitric  acid. 

(2)  The  calcium  salt  of  sulphuric  acid. 

(3)  The  silver  salt  of  hydrochloric  acid. 

(4)  The  magnesium  salt  of  malic  acid. 

(5)  The  potassium  salt  of  nitrous  acid. 

(6)  The  sodium  salt  of  carbonic  acid. 

(7)  The  two  iron  salts  of  hydrochloric  acid. 

(8)  The  calcium  salt  of  sulphurous  acid. 

(9)  The  two  iron  salts  of  sulphuric  acid. 

(10)  The  two  mercury  salts  of  hydrochloric  acid. 

4.  Write  the  formulas  of  the  salts  of  Exercise  3. 

5.  Write   the  names  of   the  compounds  represented  by  the 
following  formulas : 

(i)H2S04  (2)HC1  (3)HN03  (4)  HC2H3O2 

(5)  CaS04  (6)  Fe2(S04)3  (7)  Ag2SO4  (8)  HgNO3 

(9)  Hg(N03)2  (10)  AuCl3  (n)  FeS04  (12)  KI 

(13)  PbS  (14)  PbSO4  (15)  Na2SO;  (16)  KNO3 

(i7)KN02  (i8)Mg(N02)2  (i9)Mg(N03)2  (20)  CaC4H405 


go 


ELEMENTARY  HOUSEHOLD   CHEMISTRY 


6.    Write  formulas  of : 

(i)  Oxalic  acid 
(3)  Calcium  oxalate 
(5)  Silver  chloride 
(7)  Nitric  acid 
(9)  Calcium  nitrate 
(n)  Magnesium  acetate 
(13)  Sulphuric  acid 
(15)  Ferrous  sulphate 


(2)  Sodium  oxalate 
(4)  Hydrochloric  acid 
(6)  Magnesium  chloride 
(8)  Potassium  nitrate 
(10)  Acetic  acid 
(12)  Sodium  acetate 
(14)  Sodium  sulphate 
(16)  Potassium  bicarbonate 


CHAPTER  XV 


ALKALIES 

CONTRASTED  with  acids  in  their  effects  upon  litmus  are  the 
alkalies. 


Experiment  43. 

Materials : 
Salt 
Sugar 
Vinegar 
Alum 
Borax 


Baking  soda 
Washing  soda 
Cream  of  tartar 
Ammonia  water 
Epsom  salt 


Lemon,  slice 
Apple,  slice 
Slaked  lime 
Saltpeter 
Ferric  chloride 


Taste  each  of  the  above-named  materials  and  note  which  of 
them  are  sour.  Dissolve  the  solids  in  water.  Squeeze  out  the 
juice  of  the  lemon  and  apple.  Test  all  the  liquids  thus  obtained 
with  red  and  with  blue  litmus  paper.  Record  results  in  tabular 
form  as  follows : 


TASTE 

REACTION  TO  LITMTJS 

Sour 

Not  Sour 

Acid 

Alkaline 

Neutral 

Lemon,  etc. 

Salt,  etc. 

Alkalies 

Some  sails  affect  litmus  in  the  same  way  as  acids  —  turning 
blue  to  red.  These  are  said  to  have  an  acid  reaction.  Ex- 
amples are  alum,  zinc  sulphate,  and  cream  of  tartar.  A 
considerable  number  have  no  action  on  either  red  or  blue 
litmus.  These  are  said  to  have  a  neutral  reaction.  Salt, 
saltpeter,  and  Epsom  salt  are  neutral.  Still  others  have  an 
effect  directly  the  opposite  of  that  of  the  acids ;  that  is,  they 
turn  red  litmus  blue.  Such  are  said  to  have  an  alkaline  re- 

91 


92  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

action.     Examples  are  baking  soda   (sodium  bicarbonate), 
washing  soda  (sodium  carbonate),  and  borax  (sodium  borate). 

Experiment  44. 

Materials : 

Sodium  under  oil,  cut  in  pieces  large  enough  to  yield  a  test 
tube  of  gas  in  the  experiment.  (Cubes  of  3  mm.  or  £  inch 
are  suitable  for  a  30  cc.  test  tube.) 

Lead  foil  (tea  lead)  or  oiled  paper  in  pieces  f  inch  square. 
Caustic  soda  sticks  |  inch  long. 
Red  litmus  paper. 
Apparatus: 
Forceps. 
Dish. 

Handle  the  sodium  with  forceps,  being  careful  not  to  allow  it 
to  touch  the  hands  or  clothing.  Examine  a  freshly  cut  surface 
of  sodium  and  compare  it  with  the  lead  and  aluminium.  To  what 
class  do  all  three  of  these  substances  belong  ?  Lay  the  sodium  on 
filter  paper  for  a  few  seconds  to  free  it  from  oil,  then  wrap  it  in 
the  lead  foil  (or  oiled  paper)  leaving  a  small  opening  at  one  end. 
Fill  a  test  tube  with  water,  cover  it  with  the  thumb,  and  invert 
it  in  a  dish  of  water.  Seizing  the  wrapped  piece  of  sodium,  open 
end  up,  with  the  forceps,  bring  it  quickly  underneath  the  mouth 
of  the  inverted  test  tube.  As  the  water  enters  the  wrapping  and 
comes  in  contact  with  the  sodium,  gas  is  evolved  and  collects  in 
the  test  tube,  displacing  the  water.  When  the  action  ceases, 
again  cover  the  mouth  of  the  test  tube  and  invert  the  tube.  Re- 
move the  thumb  and  immediately  apply  a  lighted  match  or  splint 
to  the  mouth  of  the  test  tube.  What  gas  do  you  infer  to  have 
been  formed  by  the  reaction  of  the  sodium  and  water  ? 

Examine  the  liquid  left  in  the  dish,  comparing  it  with  the  water 
originally  used.  Note  its  feel  and  its  effect  on  red  litmus  paper. 

Dissolve  the  piece  of  caustic  soda  in  half  a  test  tube  of  water. 
Compare  this  solution  with  the  liquid  in  the  dish. 

To  determine  what  elements  caustic  soda  contains,  answer  the 
following  questions  and  make  Experiment  45. 

Can  the  gas  collected  in  the  present  experiment  have  been 
produced  by  decomposition  of  the  sodium?  Why?  Where 
must  the  sodium  be  at  the  end  of  the  experiment?  What  are 
the  elements  of  water?  Which  of  these  two  elements  must  be  a 
constituent  of  the  caustic  soda  ?  What  two  elements  does  caustic 


JOSEPH  BLACK.  — 1728-1799. 

A  Scottish  chemist  and  physicist,  noted  for  his  researches  upon  heat 
and  for  his  discovery  of  carbon  dioxide,  which  he  called  "  fixed  air." 
Black  explained  the  difference  between  the  mild  and  the  caustic  alkalies, 
the  relation  of  lime  to  limestone,  and  the  distinction  between  lime  and 
magnesia. 


ALKALIES  93 

soda  therefore  contain  ?    Is  it  possible  it  may  also  contain  a  third 
element?    If  so,  what? 

Experiment  45. 

Materials : 

Solutions  prepared  in  Experiment  44. 

Aluminium  foil  \  inch  X  f  inch,  two  or  three  pieces. 

(a)  Put  a  piece  of  aluminium  foil  in  a  test  tube  of  hot  water. 

(b)  Heat  the  liquid  left  in  the  dish  in  Experiment  44,  and  put 
in  a  piece  of  aluminium  foil.     What  difference  do  you  observe 
in  the  behavior  of  this  liquid  and  water  ? 

(c)  Heat  the  strong  solution  of  caustic  soda  prepared  in  Experi- 
ment 44,  drop  in  aluminium  foil,  and  cover  the  mouth  of  the  test 
tube  loosely  with  the  thumb  for  a  few  moments  to  allow  the  evolved 
gas  to  collect.     Test  this  gas  with  a  flame,  immediately  after  re- 
moving the  thumb. 

What  gas  is  produced  by  the  action  of  aluminium  on  caustic 
soda  ?  Does  aluminium  act  on  water  under  the  conditions  of 
these  experiments.  (See  (a).)  What  element  must  caustic  soda, 
therefore,  contain?  Name  the  elements  of  caustic  soda  dis- 
covered in  this  experiment  and  the  preceding  one. 

The  experiments  just  performed  have  illustrated  the  fact 
that  in  addition  to  the  alkaline  salts  there  are  some  other 
substances  which  have  an  alkaline  reaction.  These  are  the 
hydroxides  (compounds  with  oxygen  and  hydrogen)  of  the 
most  active  metals  —  sodium  hydroxide  (caustic  soda), 
potassium  hydroxide  (caustic  potash),  and  calcium  hydroxide 
(slaked  lime,  the  aqueous  solution  of  which  is  limewater). 

These  hydroxides  are  designated  the  strong  or  caustic 
alkalies  in  contradistinction  to  the  salts  of  alkaline  reaction, 
which  are  called  weak  or  mild  alkalies  —  the  former  being 
more  vigorous  than  the  latter  in  such  actions  as  characterize 
alkalies  in  general;  for  example,  in  their  effects  upon  fats, 
of  which  we  shall  learn  more  later. 

Experiment  46. 

Test  solutions  of  potassium  hydroxide  and  calcium  hydroxide 
with  red  litmus  paper.  Give  the  common  names  of  these  two 
substances. 


CHAPTER  XVI 
BASES   AND   BASIC    OXIDES 

THE  hydroxides  of  metals  are  called  bases.  The  strong 
alkalies  are  therefore  bases.  These  are  rather  exceptional 
among  bases  in  being  soluble  in  water.  The  majority  of  the 
bases  are  insoluble;  for  example,  ferric  hydroxide,  cupric 
hydroxide,  aluminium  hydroxide. 

The  insoluble  base  of  a  given  metal  (e.g.  aluminium) 
can  be  obtained  as  a  precipitate  by  adding  one  of  the  solu- 
ble bases  (sodium  hydroxide  or  potassium  hydroxide)  to  the 
solution  of  a  salt  of  the  metal  (such  as  aluminium  chloride 
or  sulphate). 

Salt  of  Metal  A  +  Base  of      =  Base  of  Metal  A    +  Salt  of  Metal  B 
Metal  B 

Aluminium  chlo-  +  Sodium        =  Aluminium  +  Sodium  chloride 

ride  hydroxide  hydroxide  (left  in  solution) 

(white  precipitate) 
A1C13  +3NaOH      =       Al(OH),  +        3  Nad 

Copper  sulphate  +  Potassium   =  Copper  hydroxide  +  Potassium     sul- 
hydroxide         (blue    precipitate)  phate 

(dissolved) 
CuSO4  +     2KOH      =       Cu(OH)2  +        K2SO4 

Ferric  nitrate       +  Calcium       =  Ferric    hydroxide    +  Calcium  nitrate 

hydroxide  (red  precipitate)  (dissolved) 

2  Fe(N03)3          +  3  Ca(OH)2  =  2  Fe(OH)3  +      3  Ca(NO3)2 

Experiment  47. 

Materials : 

Small  portions  of  the  following  solids : 
Aluminium  nitrate. 
Aluminium  sulphate. 
Copper  sulphate. 
Ferric  nitrate. 
Ferric  chloride. 

94 


BASES    AND    BASIC    OXIDES  95 

Dissolve  the  salts  in  water  in  separate  test  tubes,  labeling  the 
tubes.  Test  a  portion  of  each  solution  with  potassium  hydroxide 
solution  and  another  portion  of  each  with  sodium  hydroxide. 
Compare  the  precipitates  obtained  where  the  two  soluble  bases 
are  added  to  the  same  salt.  Also  compare  the  precipitates  ob- 
tained on  adding  the  one  soluble  base  to  two  salts  of  the  same 
metal.  Save  the  precipitates  for  use  in  Experiment  48. 

Experiment  48. 

Treat  a  very  small  portion  of  one  or  two  of  the  solutions  with 
calcium  hydroxide  solution,  using  a  much  larger  quantity  of  this 
solution  than  of  the  sodium  or  potassium  hydroxide. 

EXERCISE 

1.  Write  verbal  equations  for  the  reactions  involved  in  Experi- 
ments 47  and  48,  underscoring  the  names  of  the  precipitates. 

2.  Rewrite  the  above  equations  in  symbols,  underscoring  the 
formulas  of  the  precipitates. 

Basic  Oxides 

Most  of  the  bases  on  drying  or  heating  are  decomposed 
into  basic  oxides  and  water.  Thus : 

Base  =       Basic  oxide  +  Water 

Cupric  hydroxide  =  Cupric  oxide  +  Water 

(blue)  (black) 

Ferric  hydroxide  =  Ferric  oxide  +  Water 

Magnesium  hydroxide  =  Magnesium  oxide  +  Water 

Calcium  hydroxide  =  Calcium  oxide  +  Water 
(slaked  lime)                          (quicklime) 

With  cupric  hydroxide  this  decomposition  occurs  even 
in  the  presence  of  water,  as  is  evident  from  the  change  of 
color  which  occurs  when  the  blue  precipitate  is  heated. 

Experiment  49. 

Materials  : 

Copper  sulphate  solution. 

Specimen  of  cupric  oxide. 
To  copper  sulphate  solution  in  a  test  tube  add  sodium  hydroxide 


96  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

solution.  Note  the  color  of  the  precipitate.  What  substance  is 
it?  Heat  to  boiling.  What  change  occurs?  When  this  sub- 
stance is  dried,  it  is  found  to  be  identical  with  that  obtained  by 
burning  copper  in  oxygen,  viz.  cupric  oxide,  CuO.  Compare 
the  color  of  the  heated  precipitate  with  that  of  a  specimen  of 
cupric  oxide. 

The  hydroxides  of  most  metals,  however,  do  not  show  such  a 
color  change  when  they  are  converted  into  oxides  by  the  removal 
of  water  from  their  molecules. 

In  a  few  instances  the  basic  oxide  in  the  cold  readily  recom- 
bines  with  water  to  form  the  base.  A  striking  instance  is 
that  of  calcium  oxide  (quicklime)  which  takes  up  water  with 
evolution  of  great  heat  in  the  familiar  process  of  lime  slaking 
(or  slacking). 

The  reaction : 

Calcium  hydroxide  =  Calcium  oxide  +  Water 
Ca(OH)2  CaO          -f   H2O 

is  thus  seen  to  be  a  reversible  one,  running  in  one  direction  at 
high,  but  in  the  opposite  direction  at  lower,  temperature. 

Experiment  50. 

Materials : 
Quicklime. 
Red  litmus  paper. 

Place  a  small  lump  of  good  quicklime  (say  10  grams)  in  a  porce- 
lain dish  and  add  as  much  warm  water  as  the  lime  will  absorb. 
Allow  to  stand  for  a  few  minutes.  What  change  occurs  in  the 
lime  ?  Treat  a  little  of  the  slaked  lime  with  water  in  a  test  tube 
and  test  the  water  with  red  litmus  paper. 

Experiment  51. 

Materials : 

Magnesium  ribbon,  \  inch. 
Red  litmus  paper. 

Burn  a  piece  of  magnesium  ribbon.  What  is  the  product? 
Place  this  product  in  a  dish,  add  water,  and  stir  for  some  time. 
Test  the  liquid  with  red  litmus  paper.  Account  for  the  result. 


BASES    AND    BASIC    OXIDES  97 

EXERCISE 

1.  Write  equations  for  the  reactions  of  Experiments  49,  50,  and 

Si- 

2.  Write  equations  representing  the  dehydration  of,  that  is, 
removal  of  water  from : 

(i)  Cupric  hydroxide  (2)  Ferric  hydroxide 

(3)  Ferrous  hydroxide  (4)  Magnesium  hydroxide 

(5)  Calcium  hydroxide  (6)  Aluminium  hydroxide 


CHAPTER  XVII 

REACTIONS    OF    ACIDS    WITH    BASES    AND    WITH 
BASIC   OXIDES.     IONIZATION 

Experiment  52. 

Put  into  a  clean  evaporating  dish  about  10  cc.  (|  test  tube) 
sodium  hydroxide  solution  and  a  piece  of  litmus  paper.  Slowly 
add  dilute  hydrochloric  acid,  stirring  constantly,  until  the  color 
of  the  paper  is  permanently  changed.  Now  add  a  few  drops  more 
of  the  sodium  hydroxide  solution,  then  a  few  more  of  the  hydro- 
chloric acid  solution,  noting  the  effect  on  the  color  of  the  paper. 

Leaving  the  mixture  finally  just  acid,  take  out  the  paper,  place 
the  dish  on  a  wire  gauze  over  a  burner,  and  evaporate  to 
dryness.  Taste  the  product.  What  is  it?  Write  an  equation 
for  the  reaction  involved  in  this  experiment. 

Experiment  53. 

In  test  tubes  place  small  portions  of  solutions  of  (a)  sodium 
hydroxide,  (6)  potassium  hydroxide,  (c)  calcium  hydroxide.  Add 
litmus  solution  or  litmus  paper  and  treat  portions  of  each  solution 
with  (i)  dilute  hydrochloric  acid,  (2)  dilute  nitric  acid,  (3)  dilute 
sulphuric  acid.  Note  the  effect  on  the  litmus.  What  is  the  effect 
of  adding  more  of  the  base  ?  Write  equations  for  the  reactions  of 
this  experiment. 

In  the  above  experiments  the  acid  and  base  are  said  to 
neutralize  each  other.  In  every  case  a  salt  is  formed  and  also 
water.  The  formation  of  water  is  not  evident  because  the 
reaction  takes  place  in  presence  of  much  water.  The  for- 
mation of  the  salt  could  be  demonstrated  in  each  instance 
by  driving  off  the  water  by  evaporation,  as  was  done  in 
Experiment  52. 

The  action  of  acids  on  insoluble  bases  is  illustrated  in  the 
following  experiments. 

98 


SVANTE  AUGUST  ARRHENIUS.  — 1859-. 

The  Swedish  scientist  who  in  1887  originated  the  modern  theory  of  ionization 
of  electrolytes. 


REACTIONS  OF  ACIDS  WITH  BASES       99 

Experiment  54. 

Prepare  the  hydroxides  of  magnesium,  copper,  and  iron  (ferric 
hydroxide)  as  in  Experiment  47.  Treat  one  of  these  precipitated 
hydroxides  with  dilute  hydrochloric  acid,  another  with  dilute 
nitric  acid,  and  the  third  with  dilute  sulphuric  acid,  shaking  each 
test  tube  we^^and  allowing  time  for  the  reaction  to  complete  itself. 
How  are  the  insoluble  bases  affected  by  acids  ?  What  compounds 
are  in  solution  at  the  end  of  the  experiments?  Write  equations 
for  the  reactions  of  the  acids  on  the  bases. 

Bases,  both  soluble  and  insoluble,  then,  readily  react 
with  acids,  yielding  salts  and  water.  Thus : 

Base  +         Acid  Salt  +  Water 

Sodium  hydrox-       +  Hydrochloric  =  Sodium  chloride           +  Water 

ide                            acid  (common  salt) 
(caustic  soda) 

Potassium  hydfbx-  +  Nitric  acid  =  Potassium  nitrate        +  Water 

ide  (saltpeter) 
(caustic  potash) 

Cupric  hydroxide     +  Sulphuric  acid  =  Copper  sulphate          +  Water 

(bluestone) 

Ferric  hydroxide      +  Oxalic  acid  =  Ferric  oxalate               +  Water 

Magnesium  hy-       -j-  Sulphuric  acid  =  Magnesium  sulphate   -f-  Water 

droxide  (Epsom  salt) 

If,  as  in  the  last  three  of  the  above  examples,  the  base  is 
insoluble  but  the  salt  soluble,  the  effect  of  the  acid  is  to 
dissolve  the  base  (by  converting  it  into  salt). 

Experiment  55. 

Materials : 
Quicklime. 

Cupric  oxide,  powder. 
Magnesium  oxide  (magnesia). 

Place  small  portions  (^  gram  or  less)  of  the  above  solids  in  test 
tubes.  To  the  quicklime  add  dilute  hydrochloric  acid,  to  the 
cupric  oxide  dilute  nitric  acid,  and  to  the  magnesia  dilute  sulphuric 
acid.  Warm  gently. 

Experiment  56. 

Make  cupric  oxide  by  adding  sodium  hydroxide  to  boiling  copper 
sulphate  solution  as  in  Experiment  49.  Acidify  with  dilute 
sulphuric  acid,  and  warm. 


100  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

We  see  from  these  experiments  that  basic  oxides, 
whether  made  from  the  hydroxides  by  heating  or  from  the 
metals  by  direct  combination  with  oxygen,  react  with  acids, 
yielding  salts  and  water.  Thus : 

Basic  oxide  +         Acid  =  Salt  +  Water 

Calcium  oxide        +  Hydrochloric    =  Calcium  chloride  +  Water 

acid 

Cupric  oxide          +  Sulphuric  acid  =  Copper  sulphate  +  Water 

Ferric  oxide  -f  Oxalic  acid        =  Ferric  oxalate  +  Water 

Magnesium  oxide  +  Sulphuric  acid  =  Magnesium  sul-  +  Water 

"  phate 

Whenever  the  salt  formed  is  soluble  in  water,  the  acid 
dissolves  the  oxide.  This,  however,  is  not  simple  solution 
like  that  of  salt  or  sugar  in  water.  It  is  solution  on  account 
of  chemical  action  producing  a  soluble  product. 

EXERCISE 

Rewrite  the  above  equations,  using  symbols. 

lonization 

Solutions  of  acids,  bases,  and  salts  in  water  have  a  number 
of  characteristics  distinguishing  them  from  other  solutions, 
whether  those  others  be  aqueous  solutions  of  substances  of 
other  classes  (such  as  sugar,  alcohol,  glycerin,  or  hydrogen 
peroxide),  or  whether  they  be  solutions  in  other  solvents 
than  water. 

i.  Water  is  practically  a  non-conductor  of  electricity. 
Solutions  of  so-called  "  indifferent "  substances  (alcohol, 
sugar,  hydrogen  peroxide,  etc.)  are  also  non-conductors. 
But  aqueous  solutions  of  acids,  bases,  and  salts  conduct 
the  electric  current.  In  acting  as  conductors  these  sub- 
stances do  not  remain  unchanged  as  do  metallic  conductors 
such  as  copper  wire.  On  the  contrary,  they  undergo  con- 
tinuous decomposition  as  the  current  passes.  For  this  reason 


IONIZATION,  101 


they  are  called  electrolytic  conductors  of  "more  briefly  elec- 
trolytes (from  a  Greek  verb,  luo,  I  loose).  When  an  electric 
current  is  passed  through  a  solution  of  hydrochloric  acid, 
for  example,  chlorine  is  set  free  at  one  electrode  and  hydrogen 
at  the  other.  Again,  when  the  current  is  passed  through 
sodium  chloride  solution,  chlorine  is  set  free  at  the  same 
electrode  as  in  the  case  of  hydrochloric  acid;  at  the  other 
electrode  sodium  is,  no  doubt,  set  free,  but  it  immediately 
reacts  with  the  water,  producing  hydrogen  and  sodium  hydrox- 
ide. What  we  observe  at  the  latter  electrode,  therefore,  is 
that  hydrogen  gas  is  given  off  and  that  the  water  becomes 
alkaline,  due  to  the  production  of  sodium  hydroxide.  When 
a  current  is  passed  through  an  aqueous  solution  of  sulphuric 
acid,  the  products  obtained  are  hydrogen  at  one  electrode, 
oxygen  at  the  other.  (See  Expt.  16,  p.  12.)  This  is  quite 
consistent  with  the  supposition  that  the  primary  products 
are  hydrogen  and  the  sulphuric  acid  (or  sulphate)  radicle 
=  S(>4,  and  that  the  latter,  being  incapable  of  independent 
existence,  reacts  with  water: 

=  SO4  +  H2O  =  H2SO4  +  O 

Thus,  oxygen  is  liberated  and  the  sulphuric  acid  is  regen- 
erated. The  net  result  is,  therefore,  the  decomposition  of 
water,  and  we  ordinarily  speak  of  the  process  as  the  "  elec- 
trolysis of  water." 

The  passage  of  a  current  through  sodium  hydroxide  solu- 
tion likewise  yields  hydrogen  and  oxygen  as  final  products. 
The  primary  products  are  (a)  sodium,  which  reacts  with 
water,  liberating  hydrogen  and  regenerating  the  sodium 
hydroxide : 

Na  +  H2O  =  NaOH  +  H 

(b)  the  hydroxyl  radicle,  — OH,  which  is  immediately  con- 
verted into  water  and  oxygen : 

2  —OH  =  H2O  -h  O 


102  ELEMENTMRY   HOUSEHOLD    CHEMISTRY 

1  2. k  Reactiofts  b^tw^eil  dissolved  acids  and  bases  (neutral- 
ization) are  instantaneous.     So,  also,  are  reactions  between 
two  salts  (precipitation  reactions),  e.g.: 
Silver  nitrate  +  Sodium  chloride  =  Silver  chloride  +  Sodium   nitrate 

Reactions  between  non-electrolytes  in  solution  are  usually 
much  slower. 

3.   All  the  electrolyte  chlorides  give  the  same  precipitate 
(silver  chloride)   with  all  silver  salts.    All  sulphates   (in- 
cluding sulphuric  acid)  give  the  same  precipitate  (barium, 
sulphate)  with  all  barium  salts. 
Experiment  57. 

Materials : 

Solutions  of  sodium  chloride,  potassium  chloride,  magnesium 

chloride,  calcium  chloride,  aluminium  chloride. 
Solutions  of  silver  nitrate  and  silver  sulphate. 
Solutions  of  sodium  sulphate,  potassium  sulphate,  magnesium 

sulphate. 
Solutions  of  barium  chloride,   barium  nitrate,  and  barium 

acetate. 

Mix  a  little  of  each  chloride  solution  with  a  little  of  each  silver 
solution  (10  experiments  in  all)  and  compare  the  precipitates 
produced.  Also  mix  dilute  hydrochloric  acid  with  a  little  of  each 
of  the  silver  solutions. 

Mix  a  little  of  each  sulphate  solution  with  a  little  of  each  barium 
solution  (9  experiments)  and  compare  the  precipitates.  Also  mix 
dilute  sulphuric  acid  with  a  little  of  each  of  the  barium  solutions. 

These  and  other  peculiarities  of  electrolyte  solutions  are 
explained  by  assuming  that  when  an  electrolyte  dissolves 
in  water,  some  of  its  molecules  immediately  undergo  a  revers- 
ible decomposition  into  what  are  called  ions. 

The  mode  of  ionization  of  a  few  acids,  bases,  and  salts  is 
illustrated  by  the  following  equations : 

Hydrochloric  acid:  HC1          ^±H+  +  Cl~ 

Sulphuricacid:  H2SO4       ^±2H+  +  SO4~~ 

Acetic  acid :  HC2H3O2  ^±  H+  +  C2H3O2- 

Tartaric  acid :  H2C4H406  ^±  2  H+  +  C4H4O6— 

Citric  acid :  H3C6H5O7  ;±  3  H+  +  C6H5O7— 


IONIZATION  103 

lonization  of  bases : 

Sodium  hydroxide :       NaOH      ^±Na+      +  OH~ 
Calcium  hydroxide :     Ca(OH)2  ^±Ca  ++     +  2  OH~ 

lonization  of  salts : 

Sodium  chloride :          NaCl        ^±  Na+  +  Cl~ 

Sodium  sulphate :         Na2SO4     ^±  2  Na+  +  SO4-  ~ 

Sodium  bisulphate :      NaHSO4  ^±  Na+  +  H++  SO4~ 

Magnesium  chloride:    MgCl2      ^±Mg++  +  2  C\~ 

Magnesium  sulphate :  MgSO4      ^±Mg++  +  SO4— 

Aluminium  nitrate :      A1(N03)3  ^±  A1+++  +  3  NO3~ 

The  double  arrows,  used  in  place  of  the  usual  equality 
sign,  signify  that  the  reaction  is  a  reversible  one.  There 
are  always  present  in  the  solution  some  un-ionized  molecules 
of  the  acid,  base,  or  salt.  In  some  instances,  e.g.  acetic 
acid,  most  of  the  molecules  are  un-ionized;  in  others,  e.g. 
sodium  chloride,  there  are  only  a  few  un-ionized  molecules. 
When  a  solution  is  diluted  (by  adding  more  water),  more  of 
the  molecules  ionize.  When  the  solution  is  concentrated 
(by  evaporating  off  some  of  the  water),  some  of  the  ions 
recombine  into  molecules ;  when  it  is  evaporated  to  dryness, 
all  of  the  ions  recombine  into  molecules. 
1  All  acids  yield  the  hydrogen  ion,  H+,  as  their  positive  ion 
(cation).  The  effects  of  acids  on  litmus  may,  therefore,  be 
regarded  as  an  action  of  the  hydrogen  ion.  When  an  acid 
acts  on  a  metal,  the  hydrogen  ions  are  converted  into  mole- 
cules of  hydrogen  gas  and  the  molecules  of  metal  are  con- 
verted into  metal  ions. 

All  bases  yield  the  hydroxyl  ion,  — OH,  as  their  negative  ion 
(anion).  The  action  of  bases  on  litmus  or  other  indicators 
is,  accordingly,  a  reaction  of  the  hydroxyl  ion.  The  neutral- 
ization of  an  acid  by  a  base  involves  the  combining  of  the 
hydrogen  ions  with  the  hydroxyl  ions  to  form  water  mole- 
cules. Thus,  when  hydrochloric  acid  and  sodium  hydroxide 


104  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

solutions  are  mixed,  the  hydrogen  and  hydroxyl  ions  dis- 
appear, but  the  sodium  and  chloride  ions  remain : 

'  Na+  +  OH'  +  H+  +  Cl-  =  Na+  +  Cr  +  H2O 

When  the  insoluble  base  magnesium  hydroxide,  Mg(OH)2 
'is  acted  upon  by  hydrochloric  acid,  the  magnesium  is  con- 
verted into  ions : 

Mg(OH)2  +  2  H+  +  2  Cl-  =  Mg++  +  2  Cl-  +  2  H2O 


CHAPTER  XVIII 
METAL  TARNISHES 

MOST  metals,  when  heated  in  oxygen  or  air,  readily  com- 
bine with  the  oxygen.  The  following  are  examples  of  oxides 
formed  from  metals  in  this  way : 

Magnesium  oxide  or  magnesia,  MgO.     (See  Expt.  51,  p.  96.) 

Calcium  oxide  or  quicklime,  CaO. 

Aluminium  oxide  or  alumina,  A12O3. 

Cupric  oxide  (black),  CuO. 

Magnetic  iron  oxide  (black),  FesO^ 

Sodium  peroxide,  Na2C>2. 

In  the  presence  of  moisture  such  combination  of  metal 
with  oxygen  occurs  also  at  ordinary  temperatures,  though  at 
a  much  slower  rate  than  when  the  metal  is  heated.  In  case 
the  oxide  formed  upon  the  surface  adheres  closely  to  the 
metal,  the  oxidation  soon  comes  to  a  stop,  because  the  film 
of  oxide  prevents  the  air  coming  in  contact  with  any  more  of 
the  'metal.  Magnesium,  zinc,  and  aluminium  form  light- 
colored  tarnishes  of  this  kind,  and  consequently  retain  their 
whitish  color,  although  losing  something  of  their  metallic 
luster.  Lead  also  tarnishes  rapidly  by  oxidation,  but  the 
oxide  formed  is  darker  in  color  than  the  metal  itself. 

Experiment  58. 

Materials : 

Magnesium  ribbon. 
Zinc  sheet  or  rod. 
Aluminium. 
Lead. 

Emery  cloth. 

Polish  a  little  of  each  of  the  metals  and  compare  the  freshly 
polished  with  the  tarnished  surface. 

105 


106  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

Platinum,  gold,  and  tin  do  not  tarnish.  Nickel  tarnishes 
very  slowly,  the  tarnish  being  yellowish. 

Silver  is  not  acted  upon  by  oxygen,  or  by  any  other  con- 
stituent of  pure  air,  but  takes  a  black  tarnish  of  silver  sulphide, 
Ag2S,  when  exposed  to  the  action  of  the  element  sulphur. 
It  is  also  tarnished  in  the  same  way  by  many  compounds  of 
sulphur.  Small  quantities  of  sulphur  compounds  are  some- 
times present  in  the  air,  particularly  where  coal  is  burnt  or 
coal  gas  used  and  in  the  neighborhood  of  smelting  works. 

Silver  is  also  tarnished  by  contact  with  organic  materials 
containing  sulphur ;  for  example,  vulcanized  rubber  and  the 
proteins  of  foods  (such  as  eggs)  and  of  wool.  Silverware 
should  not  be  wrapped  in  any  fabric  containing  wool  nor  in 
bleached  or  dyed  cotton  goods  in  the  manufacture  of  which 
sulphur  may  have  been  used.  Soft  unbleached  cotton  goods 
and  tissue  paper  make  suitable  wrappings  for  silver. 

In  the  tarnishing  of  copper  the  carbon  dioxide  present 
in  the  air  plays  a  part  as  well  as  the  oxygen  and  moisture. 
The  product  is  a  carbonate  of  copper.  This  is  soluble  in 
dilute  acids  such  as  are  present  in  fruits.  Bright  copper  is 
not  acted  upon  by  such  acids.  A  bright  copper  kettle  may 
therefore  be  safely  used  in  preserving  or  other  cooking  opera- 
tions, but  not  a  tarnished  one.  Brass  and  bronze  are  alloys 
of  copper,  i.e.  materials  made  by  combining  copper  with 
other  metals  —  zinc  for  brass,  tin  (sometimes  together  with 
other  metals)  for  bronze.  The  tarnish  of  brass  and  bronze 
is  similar  to  that  of  copper. 

Removal  of  Tarnish 

The  basic  oxides  which  constitute  the  tarnish  of  most 
metals  are,  of  course,  soluble  in  suitable  acids.  But  the  use 
of  acids  for  the  removal  of  tarnish  from  metals  is  seldom 
resorted  to.  In  some  instances  it  would  be  difficult  to  find 
a  suitable  acid  —  one  that  would  dissolve  the  oxide  without 


METAL   TARNISHES  107 

attacking  the  metal.  It  has  also  to  be  remembered  that 
there  is  usually  other  dirt  to  be  removed  in  addition  to 
the  tarnish  compound  and  also  that  the  surface  of  the 
metal,  which  has  been  roughened  by  the  formation  of  the 
oxide,  must  be  polished  smooth  in  order  that  it  may  appear 
bright. 

The  polishing  of  metals  is  usually  done  with  a  cloth  or 
piece  of  soft  leather,  such  as  chamois,  and  a  fine  powder  as 
whiting,  rottenstone,  or  rouge.  When  polished  metals  are 
examined  under  the  microscope,  they  are  found  to  be  covered 
with  a  thin  film,  in  which  the  metal  behaves  more  like  a 
liquid  than  a  solid.  The  smooth,  level  film  reflects  light  just 
as  the  surface  of  mercury  does.  This  film  is  produced  by  the 
pressure  of  the  cloth  and  polishing  powder,  both  of  which  are 
softer  than  the  solid  metal.  The  presence  of  hard  particles 
in  the  polishing  powder,  and  especially  that  of  large  hard 
particles,  is  to  be  avoided.  Suitable  materials  for  polishing 
copper,  brass,  bronze  and  nickel  are  rouge,  Venetian  red, 
whiting,  putty  powder,  and  rottenstone  (called  also  tripoli). 
For  silver  and  aluminium,  which  are  softer  metals,  whiting, 
rouge,  or  putty  powder  should  be  used. 

The  polishing  powder  may  advantageously  be  mixed  into 
a  paste  with  an  oil  or  grease,  or  it  may  be  made  up  in  paste 
or  semi-liquid  form  with  a  suitable  liquid  —  either  one  that 
will  dissolve  grease  or  one  that  will  dissolve  the  tarnish 
compound.  Ammonia,  which  dissolves  the  oxides  of  copper 
and  nickel,  may  be  used  in  polishes  for  these  metals  and 
for  brass  and  bronze.  Acids,  such  as  oxalic,  citric,  cream  of 
tartar,  lemon  juice,  buttermilk,  and  vinegar  (or  vinegar  and 
salt)  are  sometimes  recommended  for  silver,  copper,  and 
brass.  Their  efficacy  doubtless  depends  upon  their  action 
on  the  oxide  films.  When  any  of  these  tarnish  solvents, 
or  polishes  containing  them,  are  used,  care  must  be  taken 
to  leave  none  of  the  active  agents  on  the  metal,  for  the 
reason  that  they  would  promote  the  oxidation  of  the  metal. 


108  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Experiment  59. 

Material : 

Copper  oxide,  powder. 

Shake  a  very  little  powdered  copper  oxide  with  ammonia  in  a 
test  tube.  Allow  to  settle  and  note  the  color  of  the  liquid. 

Experiment  60. 

Materials : 
Copper  foil. 
Whiting. 

Moisten  a  little  whiting  with  a  few  drops  of  ammonia.  Dip  a 
rag  in  this  paste  and  polish  both  sides  of  the  copper  foil.  Cut  the 
foil  into  three  pieces.  Wash  two  of  these  thoroughly.  Place  one 
of  the  washed  pieces  in  a  test  tube,  partly  cover  with  ammonia 
water,  and  leave  standing  for  a  few  minutes,  shaking  occasionally. 

Leave  the  unwashed  piece  of  foil  standing  for  a  few  hours. 
Then  compare  it  with  the  washed  piece.  Explain  the  results. 

Among  the  liquids  used  in  metal  polishes  on  account  of 
their  action  upon  grease  are  alkalies,  such  as  aqueous  solu- 
tions of  soda,  ammonia,  ammonium  carbonate,  borax,  and 
soap ;  and  hydrocarbons,  such  as  kerosene  (coal  oil),  gasoline, 
benzine,  and  turpentine.  Sometimes  both  a  hydrocarbon 
and  an  alkali  is  used,  e.g.  soft  soap  and  turpentine.1  A 
mixture  of  whiting  with  alcohol  and  a  few  drops  of  ammonia 
makes  a  good  polish  for  aluminium  as  well  as  for  silver. 

Brass  may  be  prevented  from  tarnishing  by  covering  with 
a  lacquer  which  prevents  the  air  coming  in  contact  with  the 
metal.  Lacquers  are  solutions  of  shellac  in  alcohol  (i  to  4 
ounces  shellac  to  i  pint  of  alcohol).  To  the  simple  lacquer 
various  red  and  yellow  coloring  matters  are  added.  The 
metal  to  be  lacquered  is  scrupulously  cleaned,  and  the  lac- 
quer is  very  evenly  applied  with  a  camel's-hair  brush  or  by 
dipping,  and  is  allowed  to  dry  without  being  touched. 

1  Many  recipes  for  polishing  powders  may  be  found  in  such  books  as  "The 
Scientific  American  Cyclopedia  of  Receipts,  Notes,  and  Queries "  or  Seaman's 
"  Expert  Cleaner." 


CHAPTER  XIX 
IRON   RUST 

IRON  is  at  the  present  day  the  most  useful  of  all  the  metals. 
So  large  a  part  does  it  play  in  modern  life  that  ours  has  been 
called  the  "  Iron  Age."  By  modifying  the  processes  by  which 
iron  ores  (which  are  chiefly  oxides  of  iron)  are  converted  into 
the  commercial  forms  of  the  metal  we  obtain  products  dif- 
fering considerably  in  strength  and  hardness  and  therefore 
suitable  for  different  uses.  We  have,  for  instance,  the  soft, 
tough  wrought  iron  and  mild  steel  used  in  wire,  horseshoes, 
andirons,  and  all  other  products  shaped  on  the  anvil ;  the 
hard  steel,  capable  of  being  tempered  to  various  degrees  of 
hardness  and  elasticity  for  use  in  razors,  penknives,  scissors, 
tableknives,  and  watch  springs,  and  the  brittle  cast  iron, 
more  easily  melted  than  the  other  kinds  of  iron  and  used 
in  making  objects  that  have  to  be  molded  to  a  definite 
shape,  for  example,  the  frames  and  treadles  of  sewing 
machines. 

As  compared  with  most  of  the  common  metals,  iron  has 
one  serious  defect,  the  consequences  of  which  have  always 
to  be  carefully  guarded  against.  It  tarnishes  readily,  and  the 
tarnish,  called  rust,  does  not  adhere  closely  to  the  surface 
of  the  metal,  as  do  the  tarnishes  of  magnesium,  aluminium, 
zinc,  and  copper.  Iron  rust  scales  off  and  thus  continually 
exposes  new  surface  of  metal  to  the  corroding  effect  of  the 
air.  The  prevention  of  the  corrosion  of  iron  and  steel  goods 
is,  therefore,  an  important  economic  problem. 

Iron  rust  is  a  red,  powdery  substance,  consisting  of  ferric 

109 


HO  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

oxide,  Fe2O3,  or,  strictly  speaking,  of  a  substance  inter- 
mediate in  composition  between  ferric  oxide  and  ferric  hy- 
droxide, Fe(OH)3.  It  is  therefore  a  substance  similar  to  the 
oxides  and  hydroxides  of  other  metals. 

There  are  two  general  methods  of  preventing  rusting  of 
iron.     One  is  to  keep  the  metal  dry  and  brightly  polished.     A 
rust-free  surface  rusts  much  less  readily  than  one  already 
spotted,  and  a  polished  surface  is  less  liable  to  rust  than  a 
rough  one.     Water  and  carbon  dioxide  promote  rust  forma- 
tion.    Indeed,  rust  cannot  form  in  absence  of  water.     If, 
therefore,  the  iron  is  brightly  polished  and  kept  dry,  it  wil 
not  corrode.     This  is  the  method  commonly  used  to  keej 
household  cutlery  bright.     The  more  promptly  knives  an< 
forks  are  scoured  and  dried  after  use,  the  less  labor  will 
involved  in  keeping  them  in  prime  condition. 

The  second  method  of  preventing  rusting  is  to  cover  tl 
iron  with  some  material  which  will  protect  it  from  the  air. 
A  great  variety  of  coverings  are  used  for  different  purpoj 
A  covering  of  oil  or  of  vaseline  is  sufficient  for  some  purpc 
e.g.  for  tools,  knives,  etc.,  which  are  to  be  laid  away  for  somt 
time.  Melted  paraffin  wax  may  be  used  for  the  same  pur- 
pose as  well  as  for  smoothing  irons  before  they  are  put  awa] 
on  ironing  day. 

Stoves  and  stovepipes  which  are  to  be  temporarily  stoi 
may  also  be  oiled.     But  it  is  perhaps  better  to  varnish  thei 
with  a  thin  solution  of  asphalt  in  turpentine,  which  wi] 
burn  off  when  they  are  put  into  use  again.     Common  sto> 
polish  is  made  of  graphite,  a  mineral  form  of  the  element 
carbon,  which  burns  very  slowly,  and  without  odor.     Otht 
names  for  graphite  are  plumbago  and  black  lead.1 

1The  word  "graphite"  is  derived  from  the  Greek  grapho,  I  write,  and  tl 
word  "plumbago"  from  the  Latin,  plumbum,  lead.  All  three  names  —  graphitt 
plumbago,  and  black  lead  —  are  derived  from  the  circumstance  that  this  fc 
of  carbon  is  so  soft  that,  like  lead,  it  will  mark  on  paper.  "  Lead  "  pencils 
made  of  a  mixture  of  graphite  with  clay. 


IRON    RUST  III 

More  permanent  coatings  for  iron  are  paint,  japan,  enamel, 
and  less  corrodible  metals.  Paint  is  used  on  the  structural 
steel  of  bridges,  as  well  as  on  wagons,  agricultural  machinery, 
and  other  outdoor  hardware ;  also  on  water-pipes  and  some 
other  indoor  articles.  Carriage  hardware,  tea  trays,  the 
handles  of  scissors,  and  many  other  small  articles  are 
japanned,  i.e.  covered  with  a  lacquer,  which  is  then  baked 
on,  polished,  and  varnished. 

Enamelware  is  now  very  commonly  used  in  the  kitchen. 
This  is  iron  covered  with  a  glaze  similar  to  that  used  on 
porcelain  and  chinaware.  It  is  put  on  in  a  molten  condi- 
tion, and  solidifies  on  cooling.  Enamelware  is  particularly 
satisfactory  for  culinary  vessels,  as  it  resists  the  action  of  the 
acids  contained  in  foods,  as  well  as  that  of  the  oxygen  of  the 
air.  In  using  enamelware  care  should  be  taken  not  to  crack 
the  enamel  by  shock  or  by  too  rapid  heating  or  cooling  of  the 
dry  vessel. 

Among  the  metals  used  to  cover  iron  to  protect  it  from  the 
air  are : 

(a)  Zinc.     Iron  covered  with  zinc  is  said  to  be   "  gal- 
vanized."    The  word  is  derived  from  the  name  of  Galvani, 
the  discoverer  of  the  electric  current,  but  the  modern  pro- 
cesses of  galvanizing  iron  consist  simply  in  immersing  the 
cleaned  iron  in  molten  zinc,  passing  the  sheet  between  rollers, 
and  allowing  to  cool. 

(b)  Tin.     Ordinary  tinware  is  made  of  "  tinplate,"  which 
is  sheet  iron  covered  with  tin  by  a  process  similar  to  that  used 
with  zinc. 

(c)  Nickel.     Iron  is  sometimes  nickel-plated,  the  nickel 
being  welded  to  the  iron. 

The  magnetic  oxide  of  iron,  FesCX,  formed  by  the  action 
of  atmospheric  oxygen,  or  by  that  of  very  hot  steam,  on  hot 
iron,  adheres  closely  to  the  iron.  In  this  respect  it  differs 
from  rust,  but  it  resembles  the  oxides  of  other  metals.  This 
fact  has  been  utilized  to  prevent  rusting.  The  iron  is  heated 


112  ELEMENTARY    HOUSEHOLD    CHEMISTRY 


in  a  furnace  and  superheated  steam  is  blown  in  upon  it.     Iron 
with  a  blue  finish  has  been  so  treated. 

When  once  the  covering  layer  is  broken  at  a  single  point, 
tinware  and  nickelware  will  rust  more  rapidly  than  iron  which 
has  not  received  a  protective  coating.  The  same  is  true  of 
iron  covered  with  magnetic  oxide,  and  probably  also  of 
enamelware.  Galvanized  iron,  however,  when  similarly 
injured,  does  not  corrode  as  fast  as  unprotected  iron. 
The  zinc  appears  to  exert  a  protective  action,  even  upon  the 
exposed  parts  of  the  iron.  This  is  one  reason  why  gal- 
vanized iron  is  preferred  to  tinware  for  outdoor  use.  On  the 
other  hand,  zinc  is  acted  upon  by  vegetable  acids.  Hence 
galvanized  iron  is  not  suitable  for  culinary  vessels  or  for 
receptacles  for  soft  fruits,  milk,  or  any  acid  food. 

Rust   Stains   on  Fabrics 

Linen,  cotton,  and  other  textiles  not  infrequently  become 
soiled  with  iron  rust.  Iron-rust  stains  are  sometimes  called 
"  iron  mold,"  possibly  on  account  of  some  confusion  with 
mildew,  which  is  really  a  mold.  Being  composed  of  ferric 
oxide,  which  is  insoluble  in  water  and  in  alkalies,  such  stains 
are  not  removed  by  the  ordinary  washing  processes.  Like 
other  basic  oxides,  however,  iron  oxide  is  converted  into  sol- 
uble salts  by  the  action  of  suitable  acids. 

Experiment  61. 

Materials : 
Oxalic  acid. 
Acid  potassium  oxalate. 

Heat  about  10  cc.  (f  test  tube)  of  ferric  chloride  solution  to 
boiling  and  add  sodium  hydroxide  solution.  What  is  the  precipi- 
tate ?  Write  equation  for  the  reaction  by  which  it  was  produced. 

Allow  the  precipitate  to  settle,  pour  off  the  supernatant  liquid, 
add  water,  shake,  allow  to  settle,  and  again  pour  off.  (This  is 
called  washing  by  dccantation.}  Finally  add  a  half  test  tube  of 
water,  shake  thoroughly,  and  divide  into  five  equal  portions  in  test 


IRON   RUST  113 

tubes.  To  these  add  respectively:  (i)  dilute  hydrochloric  acid, 
(2)  dilute  sulphuric  acid,  (3)  acetic  acid,  (4)  oxalic  acid,  dissolved 
in  hot  water,  (5)  acid  potassium  oxalate,  dissolved  in  hot  water. 
Which  of  these  acids  dissolve  the  precipitate  ?  Write  equations  for 
reactions.  (In  the  last  reaction  potassium  oxalate  is  formed  as 
well  as  ferric  oxalate.) 

The  acid  chosen  for  the  removal  of  rust  stains  from  tex- 
tile fabrics  must  be  one  that  will  do  the  work  quickly  and 
thoroughly  but  without  injury  to  the  textile  itself. 

Those  most  commonly  employed  are  oxalic  acid,  H2C2O4, 
and  its  acid  potassium  salt,  KHC2O4.  This  acid  salt  is  com- 
monly known  as  "  salt  of  lemon  "  or  "  salts  of  lemon,"  al- 
though actually  oxalic  acid  does  not  occur  in  lemons.  Salt 
of  sorrel  is  a  more  appropriate  name.  The  action  of  this 
salt  is  less  vigorous  —  both  on  the  rust  and  on  the  fabric  — 
than  that  of  free  oxalic  acid. 

Any  of  the  acids  used  to  remove  rust  stains  may  injure 
the  fabric  if  not  thoroughly  washed  out.  As  the  fabric  dries, 
the  acid  solution  becomes  more  and  more  concentrated  until 
it  reaches  a  concentration  at  which  it  acts  upon  the  textile 
fibers  and  weakens  them.  This  may  occur  even  with  the 
volatile  acid,  hydrochloric,  which  may  reach  the  concentra- 
tion of  20  per  cent  hydrochloric  acid  before  drying  off  com- 
pletely. Goods  which  have  been  treated  with  acid  for  the 
removal  of  rust  stains  should  be  washed  immediately  in  pure 
water,  and  afterwards  in  water  containing  a  little  ammonia. 


CHAPTER  XX 

STRONG  AND   WEAK  ACIDS  AND   BASES 

Experiment  62.* 

Materials : 

3  equal  pieces  of  magnesium  ribbon,  each  weighing  about  0.04 

gram. 

Lead  foil,  e.g.  tea  lead. 
3  eudiometer  tubes,  50  cc. 
3  dishes,  e.g.  glass  evaporating  dishes. 
Stands  and  clamps. 
Normal  (or  approximately  normal)  solutions  of  hydrochloric, 

acetic,  and  formic  acids.1 

Fill  one  eudiometer  tube  with  each  acid  solution,  invert  it  in  a 
dish  of  the  same  acid,  and  cl^mp  it  with  the  mouth  a  little  below 
the  surface  of  the  liquid  in  the  dish.  Attach  each  of  the  pieces 
of  magnesium  ribbon  to  a  piece  of  lead  foil  (e.g.  by  passing  it  through 
a  slit  in  the  latter)  so  that  the  magnesium  cannot  rise  in  the  liquid. 
Bring  the  anchored  pieces  of  ribbon  quickly  beneath  the  mouths 
of  the  eudiometers  and  compare  the  rates  at  which  the  hydrogen 
gas  collects  in  the  eudiometers. 

Experiment  63. 

Materials : 

The  normal  acid  solutions  used  in  Experiment  62. 
3  pieces  of  marble  of  about  equal  size  and  form. 

1  If  the  laboratory  reagents  are  on  the  normal  system,  the  two  former  can 
be  made  by  diluting  the  reagent  dilute  hydrochloric  and  acetic  acids.  A  normal 
solution  of  formic  acid  may  be  made  from  pure  formic  acid  (specific  gravity  1.22) 
by  diluting  37.7  cc.  to  i  liter;  and  from  acid  of  specific  gravity  1.06  by  diluting 
173.6  cc.  to  i  liter.  Normal  acetic  acid  may  be  made  by  diluting  57.1  cc.  of 
glacial  acetic  acid  to  i  liter.  Normal  hydrochloric  acid  may  be  made  as  follows : 
Dilute  105  cc.  concentrated  acid  or  165  cc.  of  acid  of  specific  gravity  i.io  to  i 
liter.  Compare  the  solution  so  obtained  with  a  normal  solution  of  sodium 
carbonate  —  53  grams  of  the  pure,  dry  salt  to  i  liter  —  by  adding  to  the  latter 
two  or  three  drops  of  methyl  orange  solution  and  running  in  the  acid  from  a 
burette  until  the  well-mixed  solution  is  just  red.  Then  dilute  the  acid  solution 
to  such  a  strength  that  10  cc.  of  it  will  exactly  neutralize  10  cc.  of  the  normal 
sodium  carbonate  solution. 

114 


STRONG  AND   WEAK  ACIDS   AND   BASES  115 

Put  the  three  pieces  of  marble  in  separate  test  tubes  and  pour 
one  acid  on  each.  Compare  the  rates  at  which  gas  (carbon  dioxide) 
is  evolved,  and  also  the  rates  at  which  the  marble  is  dissolved. 
Do  the  three  acids  arrange  themselves  in  the  same  order  with 
respect  to  their  activity  in  dissolving  marble  as  they  did  with 
respect  to  their  activity  in  dissolving  magnesium? 

Some  acids  are  much  more  active  than  others.  If  we 
take  two  quarts  of  water  and  dissolve  in  one  enough  hydro- 
chloric acid,  in  the  other  enough  acetic  acid,  to  yield  one  cubic 
foot  of  hydrogen  gas  by  their  action  on  zinc  or  magnesium, 
the  hydrochloric  acid  will  produce  the  gas  much  more  rapidly 
than  the  acetic,  although  ultimately  the  same  quantity  will 
be  set  free  from  both.  Hydrochloric  acid  also  excels  acetic 
in  the  speed  of  its  action  upon  metallic  oxides  (such  as  mag- 
nesia, cupric  oxide,  etc.)  and  upon  marble. 

Compared  in  these  and  many  other  ways,  hydrochloric 
acid  is  always  found  to  be  more  active  than  acetic.  For  this 
reason  it  is  designated  a  strong  acid,  whereas  acetic  acid  is 
classed  as  weak.  The  relative  strengths  of  other  acids  may 
be  similarly  compared,  and  by  methods  not  very  different 
the  relative  strengths  of  bases  may  be  compared.  The  results 
of  such  comparison  lead  to  the  following  classification : 

Acids : 

Strong :  Hydrochloric,  Nitric,  Sulphuric. 
Moderately  strong :  Oxalic,  Tartaric,  Citric. 
Weak :  Acetic,  Palmitic,  Stearic,  Oleic. 
Very  weak:  Carbonic,  Boric  (or  Boracic). 

Bases : 

Strong :  Sodium  hydroxide  (caustic  soda),  Potassium  hy- 
droxide (caustic  potash),  Calcium  hydroxide  (slacked 
lime  —  in  aqueous  solution,  limewater). 

Moderately  strong :  Magnesium  hydroxide. 

Weak :  Ammonium  hydroxide. 


Il6  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Very  weak :   The  hydroxides  of  copper,  iron,  aluminium, 

and  most  other  metals. 
The  student  should  memorize  the  above  classification. 


lonization  Theory  of  the  Strength  of  Acids  and  Bases 

According  to  the  theory  of  ionization,  as  we  have  seen 
(p.  103),  the  characteristics  common  to  all  acids  in  aqueous 
solution  are  due  to  the  hydrogen  ion  contained  in  all  these 
solutions.  Accordingly,  the  more  ionized  hydrogen  there 
is  in  a  given  volume  of  water  the  more  marked  will  these 
characteristics  be.  The  "  normal "  solutions  of  hydrochloric, 
formic,  and  acetic  acid  used  in  Experiments  62  and  63  con- 
tain equal  quantities  of  ionizable  hydrogen  in  a  given  volume, 
viz.  i  gram  per  liter.  But  the  hydrochloric  acid  solution  had 
more  of  this  hydrogen  actually  ionized  than  either  of  the 
others.  This  is  evidenced  not  only  by  the  greater  activity 
of  the  hydrochloric  acid,  but  also  by  the  fact  that  a  normal 
solution  of  hydrochloric  acid  is  a  very  much  better  conductor 
of  electricity  than  a  normal  solution  of  formic  or  of  acetic 
acid.  It  is  the  ions  which,  traveling  through  the  solution, 
conduct  the  electric  current.  The  un-ionized  molecules 
play  no  part  in  conduction.  The  superior  conducting  power 
of  the  hydrochloric  acid  solution  is  largely  due  to  the  great 
proportion  of  ionized  molecules  present  in  its  solution  as 
compared  with  those  in  normal  solutions  of  the  formic  and 
acetic  acids.  It  is  estimated  that  in  a  normal  solution  of 
hydrochloric  acid  780  out  of  every  thousand  molecules  are 
ionized,  while  in  formic  acid  only  14  and  in  acetic  acid  only 
4  in  a  thousand  are  ionized. 

Strong  acids  are,  therefore,  highly  ionized  acids,  weak  acids 
slightly  ionized  acids.  Similarly,  strong  bases  are  highly 
ionized  and  weak  bases  only  slightly  ionized,  and  the  superior 
activity  of  the  strong  bases  is  due  to  the  greater  quantity  of 
hydroxyl  ions,  OH~,  present  in  a  given  volume  of  solution. 


CHAPTER  XXI 


HYDROLYSIS   OF   SALTS 

Experiment  64. 

Materials : 

Litmus  paper,  red  and  blue. 
Distilled  water. 

Small   quantities  of  the  following  salts:    Sodium  chloride 
(salt) ;  sodium  sulphate  (Glauber's  salt) ;  potassium  nitrate 
(saltpeter) ;    sodium   carbonate   (washing  soda) ;    sodium 
borate    (borax) ;     ammonium    carbonate    (smelling   salt) ; 
ferric  chloride  (perchloride  of  iron) ;  ferrous  sulphate  (cop- 
peras) ;    aluminium  sulphate ;    soap  (contains  sodium  pal- 
mitate,  sodium  stearate,  and  sodium  oleate) ;  copper  sul- 
phate (blue  stone) ;  sodium  bicarbonate  (baking  soda). 
In  distilled  water  in  clean  test  tubes  dissolve  the  salts  named 
above,  and  test  the  solutions  with  red  and  with  blue  litmus  paper. 
Tabulate,  as  illustrated  below,  the  salts,  their  reactions  to  litmus, 
'  the  acids  and  bases  to  which  they  correspond,  and  the  relative 
strengths  of  these  latter : 


SALT 

Aero 

BASE 

Name 

Reaction 

Name 

Strength 

Name 

Strength 

Stannous 
chloride 

Acid 

Hydro- 
chloric 

Strong 

Stannous 
hydroxide 

Weak 

Look  over  your  results  and  state  what  general  relations  there 
are  between  the  reactions  of  salts  and  the  relative  strengths  of  the 
acids  and  bases  to  which  they  correspond. 

When  the  salt  of  a  weak  acid  or  the  salt  of  a  weak  base 
is  dissolved  in  water,  the  water  acts  upon  the  salt,  partially 
reversing  the  action  by  which  the  salt  and  water  are  formed 

117 


Il8  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

from  acid  and  base.     That  is  to  say,  the  following  reaction 
takes  place  upon  a  part  of  the  dissolved  salt : 

Salt  +  Water  =  Acid  +  Base 

This,  it  will  be  noticed,  is  the  reverse  of  the  reaction  of 
acid  with  base  which  we  studied  in  Chapter  XVII. 

Whenever  a  compound  is  acted  upon  by  water  with  the 
production  of  two  new  compounds,  it  is  said  to  be  hydrolyzed 
(literally,  split  up  by  Jie  action  of  water).  Thus,  in  the  above 
reaction,  the  salt  is  said  to  undergo  hydrolysis. 

Now,  if  the  salt  is  one  of  a  weak  base  with  a  weak  acid  (e.g. 
aluminium  carbonate),  it  may  be  completely  decomposed  by 
the  action  of  water. 

Experiment  65. 

To  ferric  chloride  solution  add  sodium  carbonate  solution. 
Note  the  immediate  formation  of  a  precipitate,  and  watch  for  sub- 
sequent action.  Test  the  gas  evolved  with  a  film  of  limewater 
in  the  glass  loop.  (See  Expt.  5,  p.  5.) 

Carbonic  acid,  when  it  is  formed,  soon  breaks  up  into  water 
and  carbon  dioxide : 

H2C03  =  H20  +  CO2 

If  the  precipitate  is  examined  after  this  action  ceases,  it  is  found 
to  be  the  base,  ferric  hydroxide,  Fe(OH)3. 

Make  the  same  experiment  with  aluminium  sulphate  instead  of 
ferric  chloride.  The  white  precipitate  remaining  in  the  test  tube 
after  the  action  ceases  is  the  base,  aluminium  hydroxide.  Write 
equations  representing  the  hydrolysis  of:  (a)  ferric  carbonate, 
(b)  aluminium  carbonate. 

If  the  salt  treated  with  water  is  one  of  a  weak  base  with  a 
strong  acid,  it  is  not  completely,  But  only  partially,  hydrolyzed, 
but  the  water  acquires  an  acid  reaction  from  the  strong  acid 
produced.  Examples  are  aluminium  sulphate,  ferric  chloride, 
and  copper  nitrate.  Solutions  of  these  salts  turn  blue  litmus 
red. 

If  the  salt  corresponds  to  a  strong  base  and  a  weak  acid. 


HYDROLYSIS  OF  SALTS  119 

it  is  partially  hydrolyzed  and  imparts  an  alkaline  reaction 
to  the  water.  Examples  are  sodium  carbonate  (washing 
soda)  and  sodium  borate  (borax).  Solutions  of  these  turn 
red  litmus  blue.  These  are  the  mild  alkalies  previously 
referred  to  (p.  93). 

Salts  of  strong  acids  with  strong  bases  are  not  hydrolyzed. 
Their  solutions  are  quite  neutral,  like  water  itself.  Examples 
are  sodium  chloride  (common  salt),  sodium  sulphate  (Glau- 
ber's salt),  and  potassium  nitrate  (saltpeter). 

The  effect  of  water  on  the  salt  of  a  weak  base  and  a  strong 
acid  is  well  illustrated  in  the  following  experiments  with 
a  substance  much  used  in  the  household,  viz.  soap.  Hard 
soap  is  a  mixture  of  the  sodium  salts  of  the  three  weak  acids, 
palmitic,  stearic,  and  oleic.  Soft  soap  is  a  mixture  of  the 
potassium  salts  of  these  same  acids. 

EXERCISE 

1.  Write  the  names  of  these  sodium  and  potassium  salts. 

2.  Write  equations  for  the  hydrolytic  reactions  studied  in  Ex- 
periment 64. 

Experiment  66. 

Materials : 

Soap,  good  quality,  in  shavings. 
Phenolphthalein  solution. 

Phenolphthalein  is  an  indicator,  i.e.  a  substance  which,  like 
litmus,  has  a  different  color  in  acid  solution  from  what  it  has  in 
alkaline  solution.  It  is  used  in  this  experiment  in  preference  to 
litmus  because  it  is  soluble  in  alcohol,  whereas  the  active  con- 
stituent of  litmus  is  not.  To  discover  what  color  the  phenol- 
phthalein  takes  in  acid,  neutral,  and  alkaline  solutions,  add  a  drop 
or  two  of  the  solution  of  this  indicator  to  (a)  a  little  dilute  acid, 
(b)  a  little  distilled  water,  (c)  a  little  dilute  alkali. 

Dissolve  a  little  of  the  soap  in  warm  water  and  a  little  in  alcohol. 
Add  a  drop  or  two  of  phenolphthalein  to  each  solution.  What 
difference  is  observed?  Now  add  water  to  the  alcoholic  solution. 
What  change  occurs  ?  What  do  you  infer  as  to  the  action  of  water 
on  the  soap  salts? 


120  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Poorly  made  soap  may  contain  some  "  free  alkali  ",  i.e. 
sodium  hydroxide.  This  can  be  determined  by  dissolving 
the  soap  in  alcohol  and  adding  a  drop  or  two  of  phenol- 
phthalein  solution.  Good  soap  will  not  give  a  color.  Soap 
containing  free  alkali  will  yield  a  pink  color. 

Experiment  67. 

Materials : 

Samples  of  commercial  and  homemade  soaps. 

Test  these  soaps  for  free  alkali  by  dissolving  them  in  alcohol 
in  clean  water-free  test  tubes  and  adding  a  drop  or  two  of  phenol- 
phthalein  solution. 


CHAPTER  XXII 
HARD  WATER 

SOME  natural  waters  are  called  hard  on  account  of  the 
difficulty  experienced  in  washing  with  them.  Soap  added 
to  such  waters  causes  the  separation  of  a  curdy  precipitate. 

Experiment  68. 

Materials : 

A  solution  of  soap  in  water. 
Hard  water. 

Solutions  of  calcium  chloride  and  calcium  sulphate. 
To  separate  portions  of  the  soap  solution  add   (i)   calcium 
chloride  solution,  (2)  calcium  sulphate  solution,  (3)  hard  water. 
Note  the  curdy  precipitate  which  rises  to  the  top  of  the  liquid. 

The  precipitate  produced  when  soap  solution  is  mixed 
with  the  hard  water  is  identical  with  that  produced  when  it 
is  mixed  with  a  solution  of  calcium  chloride,  calcium  sul- 
phate, calcium  nitrate,  or  any  other  calcium  salt.  The  re- 
action by  which  this  precipitate  is  formed  is  one  between 
the  calcium  ion  and  the  anions  of  the  soap  —  the  palmitate, 
stearate,  and  oleate  ions.  The  precipitate  consists  of  calcium 
palmitate,  calcium  stearate,  and  calcium  oleate  and  may 
appropriately  be  termed  calcium  soap.  Just  as  the  silver 
ion,  contained  in  solutions  of  silver  salts,  precipitates  the 
chloride  ion  of  potassium  chloride,  sodium  chloride,  etc., 
forming  silver  chloride  (see  p.  102),  so  the  calcium  ion,  con- 
tained in  all  solutions  of  calcium  salts,  precipitates  the  pal- 
mitate, stearate,  and  oleate  ions  of  soap  solutions,  forming 
the  insoluble  calcium  soap. 

Hard  water,  then,  is  water  containing  the  calcium  ion.1 

1  Some  hard  waters  contain  the  magnesium  ion,  which  also  produces  precipi- 
tates with  the  palmitate,  stearate,  and  oleate  ions. 

121 


122  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

The  calcium  ion  is  present  in  such  waters  because  they  have 
dissolved  some  of  the  calcium  salts  present  in  the  soil  and 
rocks  with  which  they  have  come  into  contact.  The  mineral 
called  gypsum  is  a  crystal  compound  of  calcium  sulphate  with 
water.  Its  formula  is  CaSO4  •  2  H2O.  Water  kept  in  contact 
with  this  mineral  for  a  sufficiently  long  time  will  dissolve 
about  3-015-  of  its  own  weight  of  calcium  sulphate.  If  the 
contact  is  less  prolonged,  a  smaller  quantity  of  the  calcium 
sulphate  will  be  dissolved.  Another  compound  of  very 
common  occurrence  as  a  mineral  is  calcium  carbonate.  This 
occurs  well  crystallized  as  calcite  and  in  less  pure  or  less 
clearly  crystallized  forms  as  marble,  limestone,  chalk,  and 
marl.  Small  particles  of  calcium  carbonate  are  also  com- 
monly found  in  the  soil.  Pure  water  does  not  dissolve  cal- 
cium carbonate  appreciably.1  But  water  which  percolates 
through  soil  takes  up  carbon  dioxide  from  the  soil  air  and, 
combining  with  it,  forms  carbonic  acid,  which  in  turn  combines 
with  the  calcium  carbonate,  forming  a  soluble  compound 
called  calcium  bicarbonate.  These  reactions  are  represented 
by  the  following  equations : 

CO2  +          H2O  H2CO3 

Carbon  dioxide    +        Water         =      Carbonic  acid 

CaCO3  +        H2CO3  Ca(HC03)2 

Calcium  carbonate  +  Carbonic  acid  =  Calcium  bicarbonate 

The  following  experiment  illustrates  (i)  the  formation 
of  the  insoluble  calcium  carbonate  from  carbonic  acid  and 
calcium  hydroxide,  (2)  the  formation  of  the  soluble  calcium 
bicarbonate  by  the  action  of  carbonic  acid  upon  the  carbonate. 

Experiment  69. 

Materials : 
Limewater. 

Carbon  dioxide  gas  from  generator  or  from  cylinder  of  liquid 
carbon  dioxide. 

1  It  takes  100,000  parts  of  water  to  dissolve  i  part  of  calcium  carbonate. 


HARD   WATER  123 

Graduated  cylinders,  25  cc. 
Soap  solution. 

Dilute  25  cc.  lime  water  with  an  equal  volume  of  distilled  water. 
Pass  in  carbon  dioxide.  Note  the  precipitate  of  calcium  car- 
bonate. Continue  to  pass  in  carbon  dioxide  for  some  time.  What 
happens  to  the  precipitate? 

If  the  solution  does  not  become  perfectly  clear,  filter  it.  Mix 
a  little  of  this  artificial  hard  water  with  soap  solution.  Reserve 
the  remainder  for  Experiment  70. 

Temporary  and  Permanent  Hardness 

Some  hard  waters  can  be  softened  or  partially  softened 
by  simply  boiling  them.  Hardness  that  can  be  thus  removed 
is  termed  temporary  hardness.  Temporary  hardness  is  due 
to  calcium  bicarbonate.  The  effect  of  boiling  is  to  decom- 
pose the  bicarbonate  into  calcium  carbonate  (which  pre- 
cipitates), carbon  dioxide,  and  water.  Thus: 

Ca(HCO3)2  =  CaCO3  +  CO2  +  H2O 

Experiment  70. 

Measure  into  a  test  tube  5  cc.  of  the  temporarily  hard  water 
obtained  in  Experiment  69.  Add  a  solution  of  soap,  little  by  little, 
from  a  burette  or  graduate,  covering  the  test  tube  with  the  thumb 
and  shaking  vigorously  after  each  addition.  Note  the  quantity 
of  soap  solution  required  to  give  a  lather  which  persists  for  one 
minute. 

Measure  out  a  second  5  cc.  of  the  temporarily  hard  water,  and 
boil  it  for  a  few  minutes.  What  separates  from  the  liquid?  Add 
soap  solution  from  the  burette  or  graduate  as  before,  and  note 
how  the  quantity  of  soap  required  differs  from  that  required  by 
the  unboiled  hard  water. 

Hardness  due  to  calcium  sulphate  cannot  be  removed  by 
boiling.  Such  hardness  is  termed  permanent  hardness.1 

Of  course,  the  hardness  of  the  water  of  a  given  well,  lake, 
or  river  may  be  partly  temporary  and  partly  permanent. 

1  Magnesium  bicarbonate  also  produces  temporary  hardness  and  magnesium 
chloride  and  sulphate  permanent  hardness. 


124          ELEMENTARY  HOUSEHOLD   CHEMISTRY 

That  is  to  say,  the  same  water  may  contain  both  calcium 
bicarbonate  and  other  calcium  salts,  such  as  the  sulphate. 

The  Softening  of  Water 

The  softening  of  water  consists  in  the  precipitation  of  the 
calcium  (and  magnesium)  which  it  contains.  Water  may  be 
softened  by  adding  to  it  a  salt  having  an  anion  which  com- 
bines with  the  calcium  ion  to  form  an  insoluble  compound. 
The  carbonate  of  calcium  is  insoluble.  So  if  we  add  to  hard 
water  a  soluble  carbonate,  the  calcium  will  be  precipitated  in 
the  form  of  its  carbonate.  Since  washing  soda  is  the  cheapest 
soluble  carbonate,  it  is  the  material  most  commonly  used. 
If  the  hard  water  contains  calcium  sulphate,  the  reaction  is : 

Calcium  sul-    +    Sodium  car-         =  Calcium  car-  +  Sodium  sul- 
phate bonate       .  bonate  phate 
CaSO4        +        Na2CO3           =      CaCO3        +     Na2S04 

or  in  ionic  notation : 

Ca++  +  SO4-  +  2  Na+  +  CO3-  =  CaCO3  +  2  Na+  +  SO4— 

The  calcium  being  thus  removed  from  solution  by  con- 
version into  the  insoluble  carbonate,  the  water  is  no  longer 
hard,  and  can  therefore  no  longer  act  upon  soap.  In  other 
words,  the  water  now  acts  as  a  soft  water. 

It  is,  however,  not  quite  as  satisfactory  a  laundry  water 
as  naturally  soft  water,  because  the  sodium  sulphate  left  in 
solution  has  a  slight  effect  in  precipitating  soap.  (See  Expt. 
84,  Chapter  XXVI.) 

The  action  of  borax  (sodium  borate)  in  softening  water 
is  similar  to  that  of  soda.  Calcium  borate  is  precipitated : 

Calcium   sulphate  +  Sodium  borate  =  Calcium  borate  +  Sodium  sul- 
phate 

The  calcium  is  thus  removed  from  the  water,  which  there- 
after acts  as  a  soft  water. 


HARD   WATER  125 

Temporarily  hard  water  also  can  be  softened  by  the  use 
of  soda.  The  reaction  is: 

Calcium       +       Sodium     =        Calcium      +        Sodium 
bicarbonate  carbonate  carbonate  bicarbonate 

Ca(HC03)2     +       Na2CO3     =          CaCO3       +     2  NaHCO3 

Experiment  71. 

To  5  cc.  of  the  temporarily  hard  water  add  sodium  carbonate 
solution.  Then  add  soap  solution  from  a  burette  or  graduate, 
comparing  the  quantity  required  with  that  used  with  the  un- 
treated hard  water  in  Experiment  70. 

A  method  sometimes  used  in  softening  municipal  water 
supplies  is  to  add  lime.  The  reaction  is : 

Calcium          +       Calcium       =      Calcium       +   Water 
bicarbonate  hydroxide  carbonate 

Ca(HC03)2       +       Ca(OH)2     =        CaCO3       +  2  H2O 

This  method,  however,  is  not  well  adapted  for  house- 
hold use,  since  it  is  necessary  to  measure  the  degree  of  hard- 
ness of  the  water  to  determine  just  how  much  lime  should 
be  used. 

Degrees  of  Hardness 

There  are  of  course  degrees  of  hardness  of  water,  and  the 
term  is  sometimes  given  a  strict  quantitative  signification. 
A  water  is  said  to  have  one  degree  of  hardness  when  it  has  in 
every  gallon  the  same  quantity  of  calcium  as  is  contained  in 
one  grain  of  calcium  carbonate  ;  two  degrees  of  hardness,  when 
it  has  twice  this  quantity  of  calcium  per  gallon,  and  so  on. 

It  has  been  estimated  that  each  degree  of  hardness  involves 
an  increased  consumption  of  2  to  2\  ounces  of  soap  for  every 
100  gallons  of  water.  This  quantity  of  soap  is  used  up  in 
softening  100  gallons  of  water,  and  it  is  wasted,  so  far  as  any 
useful  effect  towards  the  washing  of  clothes  is  concerned. 
Indeed,  it  is  worse  than  wasted,  since  the  precipitate  of  lime 
soap  forms  an  objectionable  stain  upon  white  fabrics.  Al- 


126  ELEMENTARY  HOUSEHOLD    CHEMISTRY 

lowing  10  gallons  of  water  per  person  per  day,  the  soap  used 
in  softening  hard  water  for  a  family  of  five  would  amount 
to  over  21  pounds  per  year  for  each  degree  of  hardness.  Many 
hard  waters  have  10  to  20  degrees  of  hardness.  It  is  therefore 
obvious  that  the  waste  may  amount  to  something  quite 
serious. 

A  hundred  gallons  of  hard  water  can  be  softened  by  the  use 
of  about  two  thirds  of  an  ounce  of  washing  soda  crystals  for 
each  degree  of  hardness.  Water  for  a  family  of  five  persons 
estimated  as  above  (50  X  365  =  18,250  gallons)  could  be 
softened  by  the  use  of  y|  pounds  of  soda  per  annum,  for  each 
degree  of  hardness.  The  7  J  pounds  of  soda  would  cost  about 
one  ninth  as  much  as  the  21  pounds  of  soap. 

With  a  water  of  a  hardness  of  10  degrees  the  comparison 
would  be  between  210  pounds  of  soap  and  75  pounds  of  soda. 
Adopting  the  wholesale  prices  of  6  cents  per  pound  for  soap 
and  2  cents  per  pound  for  soda,  we  have : 

Cost  of  softening  with  soap,  210  pounds  at  6  cents      .     .    $12.60 

Cost  of  softening  with  soda,    75  pounds  at  2  cents      .     .         1.50 

Saving  when  soda  is  used  $  1 1 . 10 

In  softening  water  with  soda,  the  use  of  too  much  soda 
should  be  avoided.  What  is  not  used  up  in  the  reaction  with 
the  calcium  compounds  is  left  in  the  water.  If  a  great  excess 
is  used,  the  water  may  be  rendered  so  strongly  alkaline  as  to 
injure  delicate  fabrics. 


CHAPTER  XXIII 

AMMONIA  AND   THE   AMMONIUM   RADICLE 

Experiment  72. 

Materials : 
Red  litmus  paper. 
Turmeric  paper. 

Pour  a  little  ammonia  water  into  a  test  tube.  Note  the  odor 
and  the  effect  produced  on  pieces  of  red  litmus  paper  and  yellow 
turmeric  paper  held  at  the  mouth  of  the  tube.  Bring  an  open 
bottle  of  concentrated  hydrochloric  acid  near  the  mouth  of  the 
test  tube.  What  forms? 

Experiment  73. 

Materials : 

Solid  specimens  of : 
Ammonium  carbonate. 
Ammonium  chloride. 
Ammonium  nitrate. 
Ammonium  oxalate. 
Ammonium  sulphate. 

Note  whether  these  salts  have  the  odor  of  ammonia.  Is  there 
an  exception  among  them?  Of  the  others,  mix  one  with  slaked 
lime  and  heat  gently,  heat  one  with  sodium  hydroxide  solution, 
and  one  with  potassium  hydroxide  solution.  Note  odor  in  each 
experiment. 

Ammonia  is  the  name  of  the  gas  of  pungent  odor  which 
escapes  from  ammonia  water  (aqua  ammonite,  liquor  am- 
monia). Ammonia  gas  is  formed  in  nature  in  the  putre- 
factive decomposition  of  animal  and  vegetable  matter  con- 
taining nitrogen.  The  odor  is  often  distinctly  perceptible 
in  horse  stables  in  which  manure  has  been  allowed  to  accu- 
mulate. 

Ammonia  was  formerly  obtained,  for  medicinal  use,  by 
destructive  distillation  of  nitrogenous  animal  wastes,  such 

127 


128 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


as  bones,  hoofs,  and  horns;  hence  the  name,  "  spirit  of  harts- 
horn," sometimes  applied  to  aqua  ammoniae.  The  com- 
pound is  now  manufactured  as  a  by-product  of  the  coal-gas 
industry.  In  the  process  of  destructive  distillation  (heating 
the  coal  in  closed  retorts)  much  of  the  nitrogen  of  the  coal 
escapes  with  the  gas  as  ammonia,  which  is  afterwards  sepa- 
rated from  the  other  constituents  of  coal  gas  and  obtained 
pure.  (See  Chapter  XII.) 

The  gas  can  be  converted  into  a  liquid  by  cold  and  pres- 
sure, and  in  this  form  is  used  in  the  refrigerating  machines 
of  cold-storage  plants  and  ice  factories.  This  anhydrous 

liquid  ammonia  is  not  to  be 
confounded  with  the  more  com- 
monly used  liquor  ammonia  — 
the  solution  of  this  gas  in 
water.  Ammonia  contains  the 
elements  nitrogen  and  hydro- 
gen and  has  the  formula  NHs. 

Experiment  74.* 

Materials : 

Ammonium  chloride. 
Slaked  lime. 
Red  litmus  solution. 
Apparatus : 

Figure  37.  Small  round- 
bottomed  flask  connected 
through  drying  tube  con- 
taining quicklime  to  upward 
delivery  tube. 

Figure  38.  Fountain  appara- 
tus, consisting  of  (a)  1-liter 
round-bottomed  flask,  fitted 
with  tightly  fitting  two- 
holed  stopper,  carrying  (i) 

a  glass  tube  reaching  nearly  to  bottom  of  flask,  (2)  a 
medicine  dropper;  (6)  a  retort  stand  with  ring  to  hold 
this  flask  in  inverted  position ;  (c)  glass  dish  or  beaker. 


FIG.  37.  —  Experiment  74.     Appa- 
ratus for  generating  ammonia. 


AMMONIA    AND    THE    AMMONIUM    RADICLE      129 


Mix  ammonium  chloride  and  slaked  lime  and  heat  gently  in 
the  generating  flask  in  the  hood,  collecting  the  gas  in  the  flask  of 
the  fountain  apparatus. 

Fill  the  medicine  dropper  with  water,  and  the  glass  dish  with 
the  red  litmus  solution. 
From  time  to  time  hold 
an  open  bottle  of  concen- 
trated hydrochloric  acid 
near  the  mouth  of  the 
inverted  flask,  and  when 
a  heavy  cloud  of  white 
fumes  is  observed,  insert 
the  rubber  stopper  and 
transfer  the  flask  to  its 
position  in  the  retort 
stand  of  the  fountain  ap- 
paratus. Press  the  bulb 
of  the  medicine  dropper 
so  as  to  force  a  few  drops 
of  water  into  the  appa- 
ratus. These  few  drops 
dissolve  practically  all 
the  ammonia  in  the  flask, 
thus  creating  a  vacuum, 
into  which  the  water  is 
then  forced  by  the  pres- 
sure of  the  air  on  the' 
water  in  the  dish.  Note 
•also  the  effect  of  the 
ammonia  on  the  litmus. 
What  does  this  indicate  ? 


Ammonia  gas  is  enor- 
mously soluble  in  water. 
One  gallon  of  water 
will  absorb  about  700 

gaUons  Of  ammonia,  or   FlG  ^-Experiment  fountain  apparatus. 
about  one  half  its  own 

weight  of  the  gas.     Thus  about  one  third  of  the  weight  of 
the  strongest  ammonia  water  consists  of  the  gas,  and  the 

K 


130  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

water  constitutes  the  other  two  thirds.  For  ordinary  house- 
hold use  much  weaker  solutions  than  this  are  sold.  Com- 
mercial "  household  ammonia  "  sometimes  contains  impurities 
which  fade  colors  or  cause  white  materials  to  turn  yellow. 
It  will  be  found  safer  and  more  economical  to  buy  concen- 
trated ammonia  from  a  druggist,  dilute  it  with  its  own  vol- 
ume of  water,  and  keep  it  in  bottles  carefully  closed  with 
glass  or  rubber  stoppers.  This  solution  can  be  further  diluted 
with  three  times  its  own  volume  of  water  for  most  house- 
hold uses.  In  pouring  ammonia  water  from  bottle  to  bottle 
discomfort  can  be  avoided  by  holding  the  bottles  above  the 
level  of  the  eyes.  The  escaping  gas,  being  lighter  than  air, 
ascends. 

The  Ammonium  Radicle 

Ammonia  water  has  an  alkaline  reaction,  and,  like  the 
hydroxides  of  metals,  neutralizes  acids,  producing  salts. 
These  facts  lead  us  to  infer  that  when  ammonia  gas  dissolves 
in  water,  it  combines  with  the  water,  forming  a  hydroxide. 

Ammonia      +     Water      =      Ammonium  hydroxide 
NH3         +       H20  NH4OH 

The  base  would  thus  be  the  hydroxide  of  a  radicle,  NH4 — , 
made  up  of  nitrogen  and  hydrogen.  To  this  radicle  the 
name  "  ammonium"  is  applied.  The  same  radicle  is  present 
in  all  ammonium  salts,  e.g.  ammonium  chloride  (sal  am- 
moniac) NHiCl,  ammonium  sulphate  (NH4)2SO4,  and  am- 
monium carbonate  (smelling  salts)  (NH4)2CO3.  In  their 
solubilities  the  ammonium  salts  are  very  similar  to  the  corre- 
sponding salts  of  potassium. 

To  include  ammonium  hydroxide  among  the  bases  we  may 
expand  our  definition  of  a  base  (see  p.  94)  into  the  fol- 
lowing : 

A  base  is  the  hydroxide  of  a  metal  or  of  a  radicle  which  plays 
the  part  of  a  metal. 


AMMONIA    AND    THE    AMMONIUM    RADICLE       131 

Ammonium  hydroxide  is  said  to  be  a  "  volatile  "  alkali, 
because  it  evaporates  without  leaving  a  residue.  This  prop- 
erty gives  it  an  advantage  over  "  fixed  "  alkalies,  such  as 
sodium  hydroxide  or  sodium  carbonate,  for  many  purposes, 
such  as  the  washing  of  window  panes  and  the  neutralization 
of  acid  stains  on  fabrics. 

Ammonium  carbonate  gradually  liberates  ammonia  and 
carbonic  acid  gases  at  ordinary  temperatures  and,  therefore, 
smells  strongly  of  ammonia.  It  is  the  basis  of  "  smelling 
salts,"  which,  as  a  rule,  contain  also  some  other  fragrant 
substance,  such  as  lavender.  Ammonium  carbonate  is 
popularly  known  as  "  crystal  ammonia."  Mixtures  of  soda 
with  just  enough  ammonium  carbonate  to  impart  an  odor 
are  sometimes  fraudulently  sold  as  "  solid  household  am- 
monia." 

Experiment  75. 

Heat  a  small  quantity  (|  gram)  ammonium  carbonate  in  a 
porcelain  dish.  What  becomes  of  the  substance?  How  could 
one  detect  soda  as  an  adulterant  of  crystal  ammonia  ? 

EXERCISES 

1.  Write  equations  for  the  reactions  obtained  in  Experiment  73. 

2.  Write   equations   for   the   reaction   of   ammonia   gas  with 
(a)  hydrochloric  acid,  (b)  nitric  acid,  (c)  sulphuric  acid,  (d)  acetic 
acid,  (e)  carbonic  acid. 

3 .  Write  equations  representing  the  neutralization  of  ammonium 
hydroxide  by  (a)  hydrochloric  acid,  (6)  sulphuric  acid,  (c)  nitric 
acid,  (</)  acetic  acid. 


CHAPTER  XXIV 

ORGANIC   RADICLES.     HYDROCARBONS  AND 
ALCOHOLS 

THE  compounds  of  the  element  carbon  (with  the  exception 
of  carbon  monoxide,  carbon  dioxide,  and  the  carbonates) 
are  called  organic  compounds.  Many  of  them  are  found  in, 
or  made  from,  animal  and  vegetable  organisms,  and  it  was 
formerly  believed  that  they  could  not  be  made  without 
the  agency  of  life.  This  is  now  known  to  be  untrue  for  many 
of  them,  but  the  term  "  organic  "  is  still  applied  to  the 
branch  of  chemistry  which  treats  of  the  very  numerous  com- 
pounds of  this  one  element,  carbon. 

Among  the  compounds  of  carbon  there  are  many  instances 
of  radicles  existing  as  the  common  constituents  of  a  number 
of  compounds,  much  in  the  same  way  as  the  ammonium 
radicle,  NELi — ,  exists  in  all  the  ammonium  salts  (see  p.  130), 
or  as  an  acid  radicle  exists  in  an  acid  and  all  its  salts  (see  p.  86). 
These  organic  radicles  may  consist  of  carbon  and  hydrogen 
in  various  proportions ;  of  carbon,  hydrogen,  and  oxygen ;  of 
carbon,  hydrogen,  and  nitrogen ;  etc. 

Among  the  simplest  and  most  frequently  occurring  or- 
ganic radicles  are  the  hydrocarbon  radicles,  consisting  of 
carbon  and  hydrogen  only.  Many  of  these  can  be  arranged 
in  classes  or  series  in  which  each  member  differs  in  formula 
from  the  preceding  one  by  one  atom  of  carbon  and  two  atoms 
of  hydrogen. 

Thus  we  have  as  one  important  series : 

The  methyl  radicle,  CH3— 
The  ethyl  radicle,  C2H5— 
The  propyl  radicle,  C3H7— 
The  butyl  radicle,  C4H9— 
The  amyl  radicle,  CsHn — 
etc.,  etc. 
132 


ORGANIC  RADICLES 


133 


The  compounds  of  the  radicles  of  such  a  series  with  any 
element,  or  with  any  other  radicle,  have  certain  points  of 
similarity,  and  there  is  a  gradual  variation  in  properties  from 
the  compounds  at  one  end  of  the  series  to  those  at  the  other 
end.  For  example,  the  compounds  of  the  above  radicles 
with  hydrogen  are  substances  which  resist  the  action  of  many 
of  the  reagents  (such  as  chlorine,  nitric  acid,  and  sulphuric 
acid)  which  act  readily  on  other  compounds  of  carbon  and 
hydrogen.  For  this  reason  they  are  called  the  paraffins 
(Latin,  parum  affinis,  possessing  little  affinity).  Petroleum 
and  its  commercial  products  —  benzine,  gasoline,  kerosene, 
and  paraffin  wax  —  are  mixtures  of  the  higher  compounds 
of  this  series.  Natural  gas  (see  Chapter  XII)  consists  chiefly 
of  the  first  member  of  the  series, — methane,  CKd, — but  also 
contains  a  little  ethane,  C2H6,  and  smaller  quantities  of  a 
few  of  the  other  members  of  the  series.  The  following  table 
of  the  densities  and  boiling  points  of  a  few  members  of  this 
series  will  illustrate  how  the  properties  of  the  compounds 
gradually  change  from  one  end  of  the  series  to  the  other. 


NAME 

FORMULA 

DENSITY  AS  A 
LIQUID 

BOILING  POINT 

Methane 

CH4 

.42 

-164° 

Ethane 

C2H6 

'      -45 

-  93 

Propane 

C3H8 

•54 

-  38 

Butane 

C4Hio 

.60 

+     i 

Pentane 

C6H12 

•63 

+  37 

Hexane 

CeHi4 

.66 

+  69 

At  ordinary  room  temperature  (20°  C.)  the  first  four 
members  of  this  series  are  gases,  those  with  5  to  10  carbon 
atoms  to  the  molecule  are  liquids,  and  the  higher  members 
of  the  series  solids.  One  has  been  made  with  60  carbon 
atoms  to  the  molecule,  i.e.  C60Hi22.  It  is  a  solid,  melting 
at  about  the  boiling  point  of  water. 


134 


ELEMENTARY  HOUSEHOLD   CHEMISTRY 


Alcohols 

When  yeast  is  allowed  to  grow  in  grape  juice  or  in  the 
"  wort "  obtained  by  extracting  malt  with  water,  the  sub- 
stance called  alcohol  (or  grain  alcohol)  is  produced.  This 
substance  is  the  characteristic  intoxicating  constituent  of  all 
liquors.  When  obtained  pure,  it  is  exactly  the  same  sub- 
stance whether  it  comes  from  cider,  wine,  beer,  or  whisky. 

A  similar  but  distinct  substance  is  obtained  as  one  of 
the  products  of  the  "  dry  "  distillation  of  wood  (heating  the 
wood  in  closed  retorts  and  cooling  the  vapors  evolved). 
This  substance  is  known  as  wood  alcohol  in  contradistinction 
to  grain  alcohol.  (Cf.  pp.  41  and  67.) 

Still  other  allied  substances  are  produced  in  very  small 
quantities  along  with  grain  alcohol  in  the  fermentation  of 
the  sugar  of  fruit  juices  or  malt  wort.  These  constitute  the 
fusel  oil  which  is  separated  from  grain  alcohol  in  the  process 
of  distillation  (which  consists  in  boiling  the  liquid  and  recon- 
densing  the  vapors  to  liquid  by  cooling). 

To  all  the  compounds  of  this  class  the  general  term  alcohols 
is  applied.  They  are  all  found  to  be  hydroxides  of  hydro- 
carbon radicles.  The  alcohols  of  the  radicles  given  above 
constitute  the  following  series: 


FORMULA 

NAME 

DENSITY 

BOILING  POINT 

CHsOH 

Methyl  alcohol 

.812 

66°  C. 

(wood  alcohol) 

C2H5OH 

Ethyl  alcohol 

.806 

78 

(grain  alcohol) 

C3H7OH 

Propyl  alcohol 

.817 

97 

C4H9OH 

Butyl  alcohol 

.823 

117 

CsHnOH 

Amyl  alcohol 

.829 

138 

As  in  the  case  of  the  hydrocarbon  series,  the  density  and 
boiling  point  of  each  member  of  the  series  are  higher  than 


ORGANIC   RADICLES  135 

those  of  the  preceding  compound.  There  is,  however,  an 
exception  in  the  density  of  ethyl  alcohol,  as  compared  with 
that  of  methyl  alcohol. 

In  that  they  are  hydroxides,  the  alcohols  resemble  the 
bases.  In  most  respects,  however,  there  is  a  marked  differ- 
ence between  the  alcohols  —  the  hydroxides  of  hydrocarbon 
radicles  —  on  the  one  hand,  and  the  bases  —  the  hydroxides 
of  metals  or  metal-like  radicles  —  on  the  other  hand.  All 
the  alcohols  are  neutral  in  reaction ;  while  all  soluble  bases 
are  alkaline.  The  simpler  alcohols,  e.g.  all  those  listed 
above,  are  liquids,  and  so  are  some  of  the  more  complex 
compounds  of  this  class;  while  the  simpler  bases,  i.e.  the 
hydroxides  of  the  metals,  are  solids,  and  only  the  more 
complex  bases,  e.g.  hydroxides  of  metal-like  radicles  such  as 
ammonium  NH4 — ,  aniline  C6H5NH3 — ,  etc.,  are  liquids,  or 
exist  in  the  dissolved  form  in  water.  Alcohols  do  not  ionize 
when  dissolved  in  water ;  bases  do. 

Experiment  76. 

Examine  specimens  of  pure  methyl  alcohol,  pure  ethyl  alcohol, 
and  amyl  alcohol.  Note  odor  of  each  and  effect  on  litmus  paper, 
red  and  blue.  Determine  for  each  whether  it  is  completely  mis- 
cible  with  water. 

Glycerol 

Just  as  there  are  bases  with  more  than  one  hydroxyl  group, 
—OH,  in  the  molecule,  e.g.  Ca(OH)2,  A1(OH)3,  so  also  there 
are  alcohols  with  more  than  one  hydroxyl  group.  The  most 
important  of  these,  in  relation  to  household  chemistry, 
is  glycerol,  known  commercially  as  glycerin  or  glycerine. 
Glycerol  is  the  hydroxide  of  the  trivalent  radicle  glyceryl, 
C3H5  =  Its  formula  is  C3H5(OH)3. 

Experiment  77. 

Examine  a  specimen  of  glycerin  (commercial  glycerol).  Note 
its  viscosity,  miscibility  with  water,  taste,  and  effect  on  red  and 
blue  litmus  paper. 


136  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Structural   Formulas 

In  organic  chemistry  it  is  a  common  thing  for  several 
compounds  to  contain  the  same  elements  in  the  same  pro- 
portions. Thus  we  have  three  different  sugars  with  the 
formula  C^H^Ou  —  cane  sugar,  milk  sugar,  and  malt  sugar. 
Such  compounds  are  said  to  be  isomers,  or  isomeric  compounds. 
In  many  instances  we  are  able  to  distinguish  isomers  from 
one  another  by  representing  their  atoms  as  differently  joined 
in  the  molecule.  Thus  the  formula,  C2H6O,  represents  two 
compounds,  viz.  ethyl  alcohol  and  dimethyl  ether.  These 
are  distinguished  as  follows : 

H  H 

I  I 

M— C— H  H— C— H 

H— C— O— H  O 

H  H— C— H 

or  C2H5OH,  H 

Ethyl  alcohol 

or  (CH3)2O 
Dimethyl  ether 

Ethyl  alcohol  is  the  hydroxide  of  the  ethyl  radicle,  while 
dimethyl  ether  is  the  oxide  of  the  methyl  radicle.     In  the 
former  the  two  carbon  atoms  are  represented  as  joined  di- 
rectly together  and  the  oxygen  atom  as  connecting  one  of  the  , 
hydrogen  atoms  to  a  carbon  atom.     In  the  latter  all  sixy 
hydrogen  atoms  are  joined  directly  to  carbon,  and  the  oxygen 
atom  unites  the  two  carbon  atoms. 

Formulas  of  this  kind  are  called  structural  or  graphic 
formulas. 

The  structural  formulas  of  all  alcohols  have  the  hydroxyl 
group,  — OH,  joined  to  a  carbon  atom  to  which  no  other 
oxygen  atom  is  attached. 


ORGANIC   RADICLES  137 

The  following  are  the  structural  formulas  of  methyl 
alcohol  and  glycerol. 

H  H 

H— C— O— H  H— C— O— H 

H  H— C— O— H 

I 
or  CH3OH,  H— C— 0— H 

Methyl  alcohol 

H 

or  C3H5(OH)3, 

Glycerol 

It  will  be  noted  that  in  all  these  formulas  the  carbon 
atom  is  represented  as  having  four  valence  bonds,  the  oxygen 
atom  two,  and  the  hydrogen  atom  one ;  thus : 

— C—  —  O—          and         H— 

I 


CHAPTER  XXV 
ESTERS.     FATS 

IN  their  behavior  towards  acids,  alcohols  resemble,  but 
differ  from,  bases.  It  will  be  remembered  that  a  base  reacts 
with  an  acid  to  give  water  and  a  product  called  a  salt.  Sim- 
ilarly, an  alcohol  reacts  with  an  acid  to  give  water  and  a 
product  analogous  to  a  salt.  For  instance 

Base  +        Acid       =  Salt  +  Water 

Sodium  hydroxide  -j-  Acetic  acid  =  Sodium  acetate  +  Water 
NaOH  +CH3COOH=     CH3COONa    +   H2O 

So  also 

Alcohol       +        Acid       =         Ester  +  Water 

Ethyl  alcohol  +  Acetic  acid  =  Ethyl  acetate     +  Water 
C2H5OH     +  CHaCOOH  =  CH3COOC2H5    +    H2O 

Thus  the  esters  bear  the  same  relation  to  acids  and  alcohols 
that  salts  bear  to  acids  and  bases.  The  ester  is  obtained 
from  the  acid  by  the  replacement  of  the  hydrogen  of  the  acid 
by  the  radicle  of  the  alcohol.  In  their  physical  properties, 
however,  esters  are  no  more  like  salts  than  alcohols  are  like 
bases.  Ethyl  acetate  and  other  esters  of  the  simpler  alcohols 
with  the  simpler  organic  acids  are  neutral,  volatile  liquors, 
with  pleasant  fruity  odors.  They  are  nearly  insoluble  in 
water  and  do  not  ionize  when  dissolved.  The  flavors  and 
odors  of  fruits  and  wines  are  in  part  due  to  the  esters  they 
contain.  Some  esters  are  manufactured  and  sold  as  flavor- 
ing matters  or  perfumes.  Amyl  acetate,  for  example,  is 
sold  as  pear  oil,  methyl  butyrate  as  pineapple  oil,  etc. 
Esters  of  more  complex  alcohols  and  acids  are  important 
constituents  of  the  waxes  —  beeswax,  Carnauba  wax,  etc. 

138 


ESTERS.      FATS  139 

Experiment  78. 

Examine  specimens  of  methyl  acetate,  ethyl  acetate,  propyl 
acetate,  amyl  acetate  (pear  oil),  methyl  butyrate  (pineapple  oil), 
ethyl  citrate,  methyl  salicylate  (oil  of  wintergreen). 

The  reactions  between  alcohols  and  acids  are  much  slower 
than  those  between  bases  and  acids.  When  ethyl  alcohol  and 
acetic  acid  are  mixed  and  kept  at  ordinary  room  tempera- 
ture, the  formation  of  ethyl  acetate  goes  on  slowly  for  several 
months.  If  the  mixture  is  kept  hot,  the  reaction  goes  on 
more  rapidly.  There  are  also  certain  substances,  such  as 
sulphuric  acid,  which  will  accelerate  the  action.  A  common 
method  of  preparing  esters  is  to  mix  the  alcohol  with  sul- 
phuric acid,  add  the  acid  whose  ester  is  wanted,  and  distill 
out  the  ester. 

Experiment  79. 

Mix  equal  volumes  of  alcohol  and  concentrated  sulphuric  acid. 
Add  acetic  acid  and  boil.  Note  the  odor  and  compare  with  those 
of  alcohol,  acetic  acid,  and  ethyl  acetate.  Has  ethyl  acetate  been 
formed  ?  Write  equations  for  the  reaction  (omitting  the  sulphuric 
acid  from  the  equation). 

Fats 

The  esters  of  the  alcohol,  glycerol,  with  certain  organic 
acids,  constitute  the  fats.  Natural  fats  and  animal  and 
vegetable  oils  —  lard,  tallow,  butter,  lard  oil,  olive  oil, 
cottonseed  oil,  linseed  oil,  castor  oil,  etc.  —  are  mixtures 
of  the  glycerol  esters  of  a  number  of  different  acids. 

The  most  common  of  these  acids  are  palmitic,  HCi6H3iO2, 
a  soft  solid;  stearic,  HCisH^A,  a  soft  solid;  and  oleic, 
HCigHssC^,  a  liquid. 

The  most  common  simple  fats  are  therefore : 

Glyceryl  palmitate,  CaHsCCieHaiC^a  known  as  palmitin  or 
tripalmitin.  This,  like  palmitic  acid,  is  a  solid. 

Glyceryl  stearate,  CaHXdgHssC^a,  stearin  or  tristearin  — 
also  a  solid. 


140          ELEMENTARY  HOUSEHOLD   CHEMISTRY 


And  glyceryl   oleate,  C3H5(Ci8H33O2)3,   olein  or  triolein  — 
a  liquid. 

Experiment  80. 

Examine  specimens  of  palmitic,  stearic,  and  oleic  acids,  and  of 
the  three  simple  fats,  tripalmitin,  triolein,  and  tristearin. 

The  structural  formula  of  ethyl  acetate  is  CH3COOC2H6, 
or 

H  H    H 

H— C— C^O— C— C— H, 

I  I       I 

H  H     H 

that  of  acetic  acid  being  CHsCOOH,  or 

H 


H— C— C— O— H 

H 

Palmitic  and  stearic  acids  belong  to  the  same  series  of 
acids  as  acetic  acid.  In  structure  they  differ  from  acetic 
acid  in  having  a  long  chain  of  carbon  atoms  (each  carrying 
two  hydrogen  atoms)  between  the  carbon  atom  of  the  CH3 — 
radicle  and  that  of  the  — COOH  radicle.1  Palmitic  acid  has 
14,  stearic  acid  16,  of  these  intermediate  carbon  atoms  in  its 
chain. 

Tripalmitin  may,  therefore,  be  represented  by  the  follow- 
ing structural  formula : 

M       /H 
CH3-(CH2)14  ^^    ^/TT 


(CH2)i4-C^-O— C— H 
/H 


CH3.(CH2)14-C^-0-C^-H 

1  The  — COOH  radicle,  called  carboxyl,  is  the  characteristic  radicle  of  organic 
acids. 


ESTERS.      FATS  141 

and  tristearin  by  a  formula  differing  from  this  in  having  16 
CH2's  instead  of  14. 

The  structural  formula  of  oleic  acid,  which  contains  two 
hydrogen  atoms  less  than  stearic  acid,  is  : 


CH3(CH2)7  •  CH=CH  •  (CH2)7COOH 

that  is  to  say,  the  middle  carbon  atoms  of  the  molecule  are 
joined  by  two  bonds  instead  of  one. 

The  structural  formula  of  triolein,  therefore,  resembles 
that  of  tripalmitin  given  above,  except  that  two  —  CH—  's 
are  inserted  between  the  seventh  and  eighth  of  the  chain  of 
CH2's. 

It  will  be  readily  understood  that  fats  may  also  be  derived 
from  the  reaction  of  two  or  three  acids  with  glycerol.  Thus 
we  might  have  an  oleo-stearo-palmitin,  derived  from  three 
fatty  acids.  Its  formula  would  be  : 


/H 

CH=CH(CH2)7C-0—  C^-H 

CH3(CH2)16C^O—  C—  H 
CH3(CH2)14 


"  Mixed  "  esters  of  this  type  are  actually  found  in  natural 
fats.  Butter,  for  instance,  has  been  shown  to  contain  a  fat 
which  is  an  ester  of  palmitic,  oleic,  and  butyric  acids,  the  last- 
mentioned  being  an  acid  of  the  same  series  as  acetic,  palmitic, 
and  stearic,  viz.  CH3(CH2)2COOH. 

The  natural  fats  are  mixtures  of  these  various  compounds, 
and  owe  their  physical  differences  to  differences  in  the  pro- 
portions of  the  individual  glycerides  which  they  contain. 
The  oils  and  more  liquid  fats  (e.g.  lard)  contain  larger  pro- 
portions of  olein,  the  more  solid  fats  (e.g.  tallow)  smaller 
proportions  of  olein  and  larger  proportions  of  stearin  and 
palmitin.  Some  of  them,  such  as  butter,  castor  oil,  linseed 


142  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

oil,  etc.,  also  contain  material  quantities  of  the  glycerol 
esters  of  other  acids  than  palmitic,  stearic,  and  oleic. 

Even  the  fat  of  two  animals  of  the  same  species  may 
differ  if  the  two  have  been  on  different  diets.  The  bacon 
from  hogs  fed  on  oats,  peas,  and  barley  is  firmer  than  that 
from  hogs  fed  on  Indian  corn  and  beans.  When  the  fat  of 
the  firm  bacon  and  that  of  the  soft  bacon  are  analyzed,  it  is 
found  that  the  former  contains  a  larger  proportion  of  stearin 
and  palmitin  than  the  latter.  In  one  investigation  the  fat 
from  soft  bacon  was  found  to  contain  four  times  as  much 
olein  as  stearin  and  palmitin  together,  while  the  fat  of  firm 
bacon  had  only  about  twice  as  much  olein  as  stearin  and 
palmitin. 


CHAPTER  XXVI 
HYDROLYSIS   OF  ESTERS.     SAPONIFICATION 

Hydrolysis  of  Esters.  —  We  have  seen  (Chapter  XXI) 
that  the  reaction  by  which  salts  and  water  are  formed  from 
weak  acids  and  bases  is  to  some  extent  reversible  —  the  salts 
reacting  with  water  to  form  acids  and  bases.  This  reaction 
of  salts  with  water  we  have  called  the  hydrolysis  of  the  salt. 

Esters  are  subject  to  hydrolysis  to  even  a  greater  extent 
than  salts.  The  products  of  such  hydrolysis  are,  of  course, 
acids  and  alcohols,  e.g. : 

Ethyl  acetate  +  Water  =  Ethyl  alcohol  -f-  Acetic  acid 
CH3COOC2H5  +  H2O     =      C2H5OH      +  CH3COOH 

The  rate  at  which  esters  react  with  water  is,  however, 
small,  unless  there  is  present  some  substance  which  has  the 
power  of  accelerating  the  reaction.  The  acids  are  one  class 
of  substances  possessing  this  accelerating  power,  particularly 
the  strong  acids,  such  as  hydrochloric  and  sulphuric.  In 
accelerating  hydrolysis  these  acids  are  not  themselves 
changed,  and  we  do  not  understand  why  they  influence  the 
rate  of  hydrolysis  of  esters.  But  the  fact  that  they  do  so  is 
well  established. 

Another  class  of  substances  having  a  similar  effect  — 
particularly  upon  the  hydrolysis  of  fats  —  is  the  class  known 
as  Upases,  a  special  division  of  a  more  general  class  of  sub- 
stances, known  as  ferments  or  enzymes.  Ferments  are  organic 
substances  possessed  of  the  power  of  promoting  reactions  be- 
tween other  substances  without  being  themselves  destroyed. 

143 


144  ELEMENTARY  HOUSEHOLD    CHEMISTRY 

Ferments  are  secreted,  some  of  them  by  microorganisms, 
others  by  plants,  and  still  others  by  special  organs  (glands)  of 
the  bodies  of  the  higher  animals.  A  ferment  of  the  lipase 
class  (sometimes  called  steapsin)  is  present  in  the  digestive 
juices  which  act  upon  foods  in  the  small  intestine.  It  has  the 
power  of  "  splitting  "  fats ;  that  is  to  say,  of  causing  them  to 
react  with  water  to  yield  fatty  acids  and  glycerol.  Though  the 
digestion  of  fats  is  not  thoroughly  understood,  it  is  believed 
that  they  are  thus  hydrolyzed  in  the  intestine,  and  that  the 
acids  and  glycerol,  after  passing  into  the  intestinal  wall,  are 
recombined  to  build  up  the  fat  of  the  body.  In  this  recom- 
bination, the  proportions  of  olein,  palmitin,  stearin,  and 
"  mixed  "  esters  formed  are  not  always  the  same  as  those 
originally  present  in  the  fat  of  the  food,  since  the  animal  may 
take  apart  the  fats  of  its  food  and  reconstruct  them  into  the 
fats  peculiar  to  its  own  species.  On  the  other  hand,  when  an 
animal  is  fattened  rapidly  on  fatty  food,  the  food  fat  may  be 
deposited  in  the  adipose  tissues  without  loss  of  its  chemical 
characteristics. 

Saponification 
Experiment  81. 

Materials : 
Ethyl  acetate. 

Dissolve  a  few  drops  of  ethyl  acetate  in  half  a  test-tubeful  of 
water.  If  not  all  the  ethyl  acetate  added  mixes  with  the  water 
on  shaking,  add  more  water  until  a  clear  solution  is  obtained. 
Divide  the  solution  into  three  exactly  equal  parts  in  three  test 
tubes  of  equal  diameter.  Into  the  test  tubes  put  respectively, 
(i)  £  cc.  dilute  sulphuric  acid,  (2)  exactly  the  same  volume  of 
the  reagent  sodium  hydroxide  solution,  (3)  exactly  the  same 
volume  of  water.  Label  the  three  test  tubes  and  place  them, 
side  by  side,  in  a  beaker  of  water  which  feels  just  warm  to  the 
hand.  Allow  to  stand,  comparing  the  odors  of  the  three  every 
five  minutes.  From  which  tube  does  the  odor  of  ethyl  acetate 
disappear  first?  What  do  you  infer  as  to  the  effect  of  sodium 
hydroxide  in  promoting  the  hydrolysis  of  ethyl  acetate?  How 
does  it  compare  with  sulphuric  acid  in  this  respect  ? 


HYDROLYSIS  OF  ESTERS.      SAPONIFICATION       145 

When  an  ester  is  treated  with  a  strong  base  (alkali),  it 
reacts  with  the  base,  forming  a  salt  and  a  free  alcohol. 

Ester          +      Base       =         Salt         +   Alcohol 
e.g.          Ethyl         +    Sodium    =      Sodium      -f-     Ethyl 
acetate  hydroxide          acetate  alcohol 

(  CH3COCp2H5  +     NaOH    =  CH3COONa  +  C2H5OH 

This  reaction  may  be  compared  with  that  of  a  strong  base 
on  an  ammonium  salt,  e.g.  that  of  sodium  hydroxide  with 
ammonium  chloride : 

NE^Cl  +  NaOH  =  NaCl  +  NI^OH 

the  sodium  salt  of  the  acid  being  formed  and  the  weak 
base  liberated.  It  may  also  be  regarded  as  a  combination 
of  hydrolysis  and  neutralization.  As  fast  as  any  free  acetic 
acid  is  formed  by  the  hydrolysis  of  the  ester 

CH3COOC2H5  +  H2O  =  CHsCOOH  +  C2H5OH 
it  is  neutralized  by  the  alkali, 

CHaCOOH  +  NaOH  =  CH3COONa  +  H2O 

The  effect  of  thus  immediately  removing  the  acid  by  neu- 
tralization is  to  accelerate  the  hydrolysis  greatly  and  also 
to  allow  the  hydrolysis  to  become  complete,  the  whole  of  the 
ethyl  acetate  being  used  up,  which  is  not  the  case  when  the 
ester  is  hydrolyzed  alone. 

When  the  ester  is  a  fat,  the  salt  formed  by  action  of  the 
base  is  a  soap.  Thus 

Fat  +       Base     =  Soap          +    Glycerol 

Glyceryl  palmi-     +     Sodium  =      Sodium  palmi-  +    Glycerol 

tate  hydroxide  tate 

(CisHgiCOO^CsHs  +  3  NaOH    =  3  C15H3iCOONa  +  C3H5(OH)3 

This  is  saponification  (soap  making)  proper,  but  the  term 
has  been  extended  in  meaning  so  as  to  include  the  reaction 
of  any  ester  with  a  base.  Hence  we  speak  of  the  saponifica- 
tion of  ethyl  acetate  as  well  as  that  of  lard  or  tallow. 


146  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Soaps 
Experiment  82. 

Materials : 

Lard. 

10  per  cent  solution  of  potassium  hydroxide  in  alcohol. 

Flask,  150  cc. 

Evaporating  dish,  6  inch. 

Water  bath. 

Weigh  out  25  grams  lard  and  introduce  it  into  the  flask.  Add 
75  cc.  alcoholic  potash.  Heat  on  a  water  bath  until  a  drop  let 
fall  into  water  dissolves  clear,  i.e.  without  leaving  any  globules  of 
fat.  Place  100  cc.  water  in  the  evaporating  dish  and  pour  the 
contents  of  the  flask  into  the  dish.  Place  on  the  water  bath  and 
evaporate  until  the  odor  of  alcohol  is  gone  and  a  pasty  residue 
remains.  Redissolve  this  residue  in  hot  water.  Note  the  feel 
of  this  solution.  To  a  small  portion  add  calcium  chloride  solution. 
Save  the  main  portion  for  Expt.  83,  and  a  small  one  for  Expt.  84. 

Experiment  83. 

Materials : 

Sodium  carbonate,  powdered. 
Potassium  bisulphate,  powdered. 

Place  a  piece  of  litmus  paper  in  the  solution  saved  from  Experi- 
ment 82  and  acidify  with  dilute  hydrochloric  acid.  Note  what 
rises  to  the  surface.  This  precipitate  consists  of  a  mixture  of  the 
fatty  acids,  the  salts  of  which  constitute  the  soap.  Write  equa- 
tions for  the  reaction  of  hydrochloric  acid  with  potassium  palmitate. 

Boil  the  liquid  and  filter  through  a  wet  filter.  The  fatty  acids 
do  not  pass  through  the  wet  filter.  To  the  filtrate  add  powdered 
sodium  carbonate,  little  by  little,  stirring,  until  the  acid  is  neu- 
tralized. Evaporate  to  dryness.  Allow  to  cool.  Stir  up  the 
residue  with  alcohol,  filter,  and  evaporate  the  alcohol  on  the  water 
bath. 

Examine  the  sirupy  residue.  Mix  a  drop  or  two  with  powdered 
potassium  bisulphate  and  heat  in  a  test  tube,  noting  odor.  Make 
the  same  test  on  glycerol,  comparing  results  with  those  obtained 
with  the  residue.  The  odor  produced  by  heating  glycerol  with 
potassium  bisulphate  is  that  of  a  substance  called  acrolein,  C3H4O. 
This  is  one  of  the  products  of  a  decomposition  of  glycerol,  the  other 
being  water : 

C3H8O3    =   C3H4O    +   2H2O 


HYDROLYSIS  OF   ESTERS.      SAPONIFICATION      147 

The  chemical  reaction  involved  in  the  manufacture  of 
soap  is  that  given  above  (p.  145),  viz. : 

Fat  +  Base  =  Soap  +  Glycerol 

For  the  preparation  of  soft  soaps  the  base  used  is  potassium 
hydroxide ;  for  the  hard  soaps,  sodium  hydroxide. 

The  fat  may  be  boiled  with  an  aqueous  solution  of  the  base, 
or  the  two  may  be  put  together  and  either  left  standing  for 
several  days  or  subjected  to  pressure  for  a  shorter  space  of 
time. 

Soaps  made  by  the  latter  method  (the  "  cold  process  ") 
contain  the  glycerol  produced  in  the  reaction.  Glycerol, 
being  an  emollient,  healing  substance,  is  an  unobjectionable 
constituent  of  toilet  soap.  In  the  boiling  process  it  is  more 
common  to  separate  the  soap  and  glycerol  by  "  salting  out  " 
the  former.  When  the  saponification  is  complete,  common 
salt  is  added  to  the  pot.  The  soap,  being  insoluble  in  salt 
solutions,  is  precipitated  and  collects  on  the  surface  of  the 
water.  Soap  made  in  this  way  is  known  as  "  curd  "  soap. 

Experiment  84. 

Heat  a  soap  solution  until  it  is  quite  clear.  Add  solid  sodium 
chloride.  Note  what  separates  from  the  liquid.  Allow  this  pre- 
cipitate to  collect  at  the  surface  of  the  liquid.  Pour  or  skim  off 
into  a  test  tube,  add  distilled  water,  and  warm.  Does  it  dissolve  ? 

In  what  respect  does  the  effect  of  sodium  chloride  on  a  soap 
solution  differ  from  that  of  calcium  chloride?  Sodium  sulphate 
has  an  effect  similar  to  that  of  sodium  chloride.  Explain  why 
permanently  hard  water  softened  with  soda  is  not  quite  as  satis- 
factory for  laundry  purposes  as  naturally  soft  water. 

The  glycerol,  which  is  left  in  solution  in  the  brine  in  this 
"  boiling  process  "  of  soap  making,  is  subsequently  refined 
and  sold  as  "  glycerin  "  for  medicinal  use  or  for  the  manu- 
facture of  explosives,  —  nitroglycerin,  dynamite,  etc. 

In  the  manufacture  of  soft  soap  it  is  customary  to  leave 
the  glycerol  in  the  soap. 


CHAPTER  XXVII 
COMMERCIAL  SOAPS 

THE  chemical  reactions  involved  in  the  manufacture 
of  soap  conform,  of  course,  to  the  law  of  definite  proportions. 
(See  Chapter  VII.)  To  saponify  a  given  weight  of  a  pure 
fat,  e.g.  glyceryl  palmitate,  a  definite  weight  of  a  pure  base, 
e.g.  sodium  hydroxide,  is  required.  If  too  much  fat  is  used, 
the  excess  will  be  left  in  the  soap  as  "  unsaponified  fat." 
If  too  much  base  is  used,  the  excess  will  remain  in  the  soap 
as  "  free  alkali."  Moreover,  since  saponification  is  a  rather 
slow  process,  it  is  quite  possible  for  a  soap  to  contain  both 
free  alkali  and  unsaponified  fat,  if  time  has  not  been  allowed 
for  the  reaction  to  run  to  completion.  Since  all  natural 
fats  are  mixtures  and  the  commercial  alkalies  used  in  soap 
manufacture  are  not  chemically  pure  substances,  it  requires 
great  skill  and  care  to  manufacture  soap  which  is  free  from 
both  unsaponified  fat  and  free  alkali.  For  rough  cleaning 
purposes,  such  as  scrubbing,  an  excess  of  free  alkali  can  be 
tolerated,  and  soap  suitable  for  such  purposes  may  be  made 
at  home.  On  painted  or  varnished  surfaces  soaps  should 
be  used  with  extreme  care,  if  at  all.  If  used,  they  should 
contain  no  free  alkali.  Scouring  powders  and  soaps  contain- 
ing much  free  alkali  are  injurious  to  aluminium  ware.  For 
laundry  purposes,  except  for  woolens  or  silks,  a  little  free 
alkali  is  permissible,  but  the  amount  should  not  be  as  much 
as  one  per  cent  of  the  weight  of  the  dry  soap.  Toilet  soaps 
and  wool  soaps  should  not  contain  any  free  alkali.  Laundry 
soaps  should  not  contain  any  unsaponified  fat. 

148 


COMMERCIAL    SOAPS  149 

Experiment  85.  —  Test  for  Unsaponified  Fat. 

Materials : 

A  number  of  samples  of  commercial  and  home-made  soaps. 

Benzine. 

An  alcoholic  solution  of  the  dye  Sudan  III. 
Finely  slice  about  5  grams  of  the  soap.  Spread  on  a  watch 
glass  and  dry  in  a  water  oven.  Place  half  the  dried  residue  in  a 
test  tube,  cover  with  benzine,  and  shake  for  some  time.  Filter 
off  the  benzine  through  a  dry  filter  on  to  a  clean  watch  glass  and 
allow  it  to  evaporate.  Evaporation  may  be  hastened  by  placing 
the  watch  glass  on  a  steam  radiator  or  on  a  steam  bath.  A  smeary 
residue  is  an  indication  of  fat.  To  confirm,  add  a  little  of  the 
Sudan  III  solution,  and  stir  with  the  smeary  residue.  Pour  off 
the  Sudan  III  from  the  watch  glass,  wash  once  with  alcohol,  and 
add  hot  water.  Globules  of  fat,  colored  pink  with  the  dye,  will 
float  on  the  water. 

Experiment  86.  —  Test  for  Free  Alkali 

Materials : 

Soaps  used  in  Experiment  85. 
Phenolphthalein  solution. 

Shake  a  portion  of  the  fresh  soap  with  alcohol  and  add  a  drop 
or  two  of  the  phenolphthalein  solution.  A  pink  color  shows  the 
presence  of  free  alkali. 

Why  may  not  the  soap  be  dissolved  in  water  for  this  test? 
(See  Chapter  XXI.) 

All  commercial  soaps  contain  more  or  less  water.  A 
well-made  soap  should  not  contain  over  25  per  cent.  Low- 
grade  soaps  sometimes  contain  35  per  cent  or  even  more; 
good  toilet  soaps  sometimes  as  low  as  13  to  15  per  cent. 

Experiment  87.  —  Determination  of  Water  Content. 

Materials : 
Soap. 

100  cc.  beaker. 
Sand. 

Water  bath. 

Air  bath  with  thermometer. 

In  an  evaporating  dish  heat  enough  of  the  sand  to  cover  the 
bottom  of  the  beaker  to  the  depth  of  half  an  inch.  Allow  to  cool. 


150  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Shave  all  the  soap  finely,  mix  well,  and  weigh  out  5  grams. 
Place  the  sand  and  a  glass  stirring  rod  in  the  beaker  and  determine 
the  weight.  Add  the  soap  and  25  cc.  or  more  alcohol.  Heat  on 
the  water  bath,  stirring  well  to  dissolve  the  soap  in  the  alcohol. 
Evaporate  to  dryness  on  the  water  bath,  then  place  in  the  air 
bath  and  regulate  the  flame  so  as  to  keep  the  temperature  con- 
stant at  110°  C.  After  one  hour  remove  the  beaker  from  the  air 
bath,  allow  to  cool,  and  weigh.  Return  the  beaker  to  the  air 
bath  for  half  an  hour.  Cool  again  and  weigh.  Repeat  until 
constant  or  nearly  constant  weight  is  attained.  Calculate  what 
percentage  of  water  the  soap  contained. 

Not  only  is  the  quantity  of  water  contained  in  a  soap  of 
interest  in  relation  to  the  price,  but  it  is  also  of  importance 
with  reference  to  the  lasting  quality  of  the  cake  or  bar. 
Moist  soap  is  soft  and  tends  to  waste  in  use.  The  drying 
of  soap  is,  therefore,  a  good  household  practice.  The  bars 
should  be  cut  into  pieces  of  convenient  size  for  use  and  kept 
in  a  warm  place,  piled  loosely,  so  as  to  allow  a  free  circulation 
of  air. 

Although  soda  soaps  are  all  classed  as  "  hard,"  there  is 
actually  a  great  deal  of  variation  in  the  hardness  of  different 
samples.  The  hardness  depends  to  some  extent,  as  we  have 
just  seen,  on  the  proportion  of  water  in  the  soap.  It  also 
depends  on  the  materials  from  which  the  soap  was  made. 
Soaps  containing  too  much  oleate  will  be  soft  and  soluble. 
Thus,  soaps  made  from  olive  or  cottonseed  oil  lather  better, 
but  waste  away  more  rapidly  than  those  made  from  the 
solid  fats,  palm  oil  and  tallow,  which  contain  a  larger  propor- 
tion of  stearate  and  palmitate. 


CHAPTER  XXVIII 
FOREIGN   INGREDIENTS    OF    COMMERCIAL    SOAPS 

WE  have  seen  that  in  addition  to  the  soaps  proper  —  i.e. 
the  salts  of  fatty  acids  —  commercial  soaps  always  contain 
water  and  may  contain  glycerol,  unsaponified  fat,  and  free 
alkali.  But  in  practice  other  substances  are  frequently 
added,  either  to  lower  the  cost  of  production  or  to 'render  the 
soap  more  attractive.  The  substances  added  to  lower  the 
cost  of  production  are  of  two  classes :  (i)  other  detergents ; 
(2)  fillers. 

Detergents 

Among  the  detergents  added  to  soaps  are : 

Sodium  and  Potassium  Carbonates.  —  These  are  cheap 
and  harsh  alkalies  and  are  to  be  regarded  as  adulterants, 
except  in  soaps  to  be  used  for  rough  cleaning.  Even  for 
such  purposes  the  soda  or  potash  can  be  more  economically 
purchased  separately,  as  soda  ash  or  washing  soda,  and  as 
pearl  ash,  respectively.  Sodium  carbonate  cannot  be  added 
to  soap  in  greater  quantity  than  5  per  cent  without  causing 
a  white  incrustation  on  the  surface  of  the  soap.  Potassium 
carbonate  can  be  added  in  larger  quantity,  and  has  the  prop- 
erty of  making  the  soap  look  finer  in  texture  and  therefore 
more  attractive. 

Experiment  88.  —  Test  for  Carbonates 

Materials : 

Soda  ash  (sodium  carbonate). 
Pearl  ash  (potassium  carbonate). 
Commercial  soaps  and  washing  powders. 

Add  a  little  dilute  sulphuric  acid  to  (i)  soda  ash,  (2)  pearl  ash. 
Note  and  account  for  the  effervescence.  Write  equations  for  the 
reactions. 


152  ELEMENTARY  HOUSEHOLD    CHEMISTRY 

Test  the  commercial  soaps  and  washing  powders  for  carbonates 
in  the  same  way. 

Sodium  silicate  is  known  as  "  water  glass."  This  substance 
gives  firmness  to  soap,  and  enables  it  to  hold  more  water  and 
still  remain  hard.  In  small  quantities  it  is  a  legitimate  ad- 
dition to  soaps  for  some  purposes.  Soaps  containing  more 
than  a  very  little  silicate,  when  used  in  the  laundry,  leave  a 
deposit  of  silica  (an  insoluble  substance  of  the  same  composi- 
tion as  sand)  in  the  clothes. 

Experiment  89.  —  Test  for  Silicate. 

Treat  the  finely  shaved  soap  with  hot  alcohol  until  nothing 
further  dissolves ;  filter  and  wash  with  hot  alcohol.  Now  wash 
the  residue  with  hot  water,  collecting  the  solution  obtained. 
Acidify  this  solution  with  hydrochloric  acid,  evaporate  to  dryness, 
and  gently  heat  the  residue  for  some  time.  If  it  chars,  heat  more 
strongly  until  it  is  completely  burned.  Allow  to  cool,  add  water 
and  a  little  hydrochloric  acid,  and  warm.  Silica  will  be  left  as  an 
insoluble,  gritty  residue. 

Sodium  Resinate. — Rosin  (also  termed  colophony)  consists 
of  acids  which  react  with  alkalies  to  form  salts  called  resinates, 
which,  like  soaps,  have  detergent  properties.  These  resi- 
nates cannot  be  used  separately  for  cleansing  purposes.  In 
dilute  hot  solutions  they  hydrolyze  to  so  great  an  extent  as 
to  precipitate  the  rosin  acids.  These  are  deposited  on  the 
goods,  causing  a  yellow  stain  having  the  odor  of  rosin.  Resi- 
nates are  often  contained  in  laundry  soaps,  particularly  yellow 
soaps,  and  are  objectionable  constituents,  unless  present 
in  only  small  quantities.  Yellow  soaps  have  been  analyzed 
which  contain  up  to  40  per  cent  of  resinates.  Soaps  con- 
taining resinates  are  sometimes  called  "  rosin  soaps  "  and  are 
spoken  of  as  containing  rosin. 

Experiment  90.  —  Test  for  Rosin. 

Materials : 

Soaps  with  and  without  rosin. 
Acetic  anhydride. 


FOREIGN   INGREDIENTS   OF  COMMERCIAL  SOAPS      153 

Compare  the  odors  of  the  soaps  containing  rosin  with  the  odors 
of  the  non-rosin  soaps.  Dissolve  the  soaps  in  water.  Acidify 
with  sulphuric  acid.  Filter.  Dissolve  the  precipitate  in  acetic 
anhydride.  What  is  this  precipitate  (i)  if  the  soap  is  pure? 
(2)  if  the  soap  contains  rosin? 

To  5  cc.  water  add  5  cc.  concentrated  sulphuric  acid.  Cool 
the  mixture.  Place  about  2  cc.  in  a  test  tube  and  add  a  few 
drops  of  the  acetic  anhydride  solution  of  the  fatty  acids.  A 
violet  coloration  shows  that  rosin  is  present. 

Petroleum  Products.  —  Petroleum  products,  such  as  paraf- 
fin wax,  kerosene,  and  naphtha  (a  volatile  product  resembling 
benzine)  are  sometimes  added  to  soap.  These,  being  fat 
solvents,  have  value  as  detergents.  Kerosene  itself  is  some- 
times used  in  the  clothes  boiler,  both  in  the  household  and  in 
commercial  laundries.  The  naphtha  soap,  however,  cannot 
be  used  with  hot_  water. 

Borax  is 'a  sodium  borate,  whose  detergent  property  is 
well  known.  It  is  an  excellent  ingredient  of  soaps. 

Fillers 

Among  the  "  fillers,"  i.e.  cheap,  weight-making  substances 
of  little  or  no  detergent  value,  used  as  ingredients  of  commer- 
cial soaps,  are  the  sulphates  of  sodium,  potassium,  calcium, 
and  barium,  infusorial  earth  (a  fine  form  of  silica,  SiO2,  left 
from  the  decay  of  minute  marine  organisms  called  infusoria), 
fine  clay,  chalk,  or  whiting  (calcium  carbonate),  French  chalk 
(a  soft,  powdery  magnesium  silicate),  starch,  and  impure 
vaseline.  In  the  detection  of  these  substances  advantage  is 
taken  of  the  circumstances  that  none  of  them  is  soluble  in 
alcohol  and  only  the  sodium  sulphate  and  potassium  sul- 
phate are  soluble  in  water. 

Experiment  91.  —  Tests  for  Fillers. 

Dissolve  the  finely  shaved  soap  in  alcohol.  Filter  and  wash 
the  insoluble  residue  with  alcohol,  rejecting  the  alcoholic  solution. 
Boil  the  residue  insoluble  in  alcohol  with  water.  Treat  the  residue 
insoluble  in  water  and  the  water  solution  as  follows: 


154 


ELEMENTARY  HOUSEHOLD    CHEMISTRY 


Residue 

Acidify  with  dilute  hydro- 
chloric acid.  Effervescence  in- 
dicates a  carbonate  such  as 
chalk  or  whiting. 

Residue  insoluble  in  dilute 
acid  may  be  calcium  sulphate, 
barium  sulphate,  silica,  clay, 
French  chalk,  etc. 


Solution 

Acidify  with  dilute  hydrochlo- 
ric acid.  Effervescence  shows 
presence  of  sodium  or  potassium 
carbonate. 

To  a  portion  of  the  acidified 
solution  add  barium  chloride.  A 
white  precipitate,  insoluble  in 
acids,  shows  the  presence  of 
sodium  or  potassium  sulphate. 

Cool  a  portion  of  the  acidified 
solution  and  add  iodine.  A  blue 
color  shows  starch. 


CHAPTER  XXIX 
SPECIAL   SOAPS  AND   SCOURING  POWDERS 

Perfumed  and  Colored  Soaps.  —  The  perfumes  and  color- 
ing matters  ordinarily  added  to  toilet  soaps  are  harmless, 
but  sometimes  excessive  quantities  of  perfume  are  used  to 
conceal  disagreeable  odors  due  to  the  use  of  decomposing 
fats.  Strongly  perfumed  soaps  are,  therefore,  to  be  regarded 
with  suspicion. 

Transparent  Soaps.  —  The  best  transparent  soaps  are 
made  by  dissolving  the  soap  in  alcohol,  filtering  off  the  un- 
dissolved  residue,  then  removing  the  alcohol  by  evaporation, 
Glycerin  is  often  added  to  give  a  pleasant  emollient  feel. 
Cheaper  transparent  soaps  are  made  by  the  cold  process 
from  tallow,  castor  oil,  palm  oil,  or  coconut  oil.  These 
usually  contain  free  alkali.  Some  contain  sugar,  an  unde- 
sirable adulterant,  because,  being  so  soluble,  it  causes  rapid 
wasting  of  the  soap. 

Experiment  92.  —  Test  for  Sugar. 

Dissolve  the  soap  in  Avater,  acidify  with  dilute  sulphuric  acid, 
filter  off  the  precipitated  fatty  acids.  Boil  the  filtrate  for  about 
half  an  hour,  neutralize  with  sodium  hydroxide,  add  a  little  of  the 
neutralized  solution  to  Fehling-Benedict  solution,  and  boil  for  a 
minute.  A  red  or  yellow  precipitate  (cuprous  oxide,  Cu2O)  shows 
sugar. 

Floating  Soaps.  —  Floating  soaps  are  made  by  beating  the 
molten  soap  to  incorporate  air  bubbles. 

Marine  Soap.  —  Marine  soap  is  a  soap  made  from  palm- 
nut  or  coconut  oil,  and  takes  its  name  from  the  fact  that 
it  will  form  a  lather  with  sea  water.  Marine  soap  has 
been  known  to  contain  as  much  as  70  per  cent  of  water. 


156  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Mottled  Soaps.  —  Soap  with  a  faint  gray  mottle  has  been 
known  for  a  very  long  time.  The  mottling  was  originally 
due  to  the  use  of  rather  impure  fats  and  alkalies.  When 
melted  soap  is  solidifying,  the  more  solid  of  its  ingredients, 
sodium  stearate  and  sodium  palmitate,  become  solid  before 
the  sodium  oleate.  Some  of  the  impurities,  such  as  iron 
salts,  tend  to  accumulate  in  the  liquid  sodium  oleate.  When 
the  soap  has  all  solidified,  the  dark-colored  impurities  are  left 
in  the  places  where  the  sodium  oleate  had  accumulated. 
This  gives  a  mottled  appearance. 

Modern  mottling,  which  is  often  much  more  pronounced 
than  the  older  kind,  is  accomplished  by  the  intentional  addi- 
tion of  coloring  matters  —  ultramarine  for  blue,  boneblack 
(carbon)  or  manganese  dioxide  for  gray,  etc.  The  mottling 
has  no  effect  on  the  quality  of  the  soap  and  has  no  bearing 
upon  its  real  value. 

Medicated  Soaps. — A  great  variety  of  medicinal  substances 
are  added  to  soaps.  Carbolic  acid,  tar,  and  oatmeal  are 
among  the  commoner  ones. 

Soap  Powders.  —  Soap  powders  are  made  by  melting  soda 
crystals  (crystallized  sodium  carbonate)  and  adding  soap. 
They  may  have  as  little  as  i  or  2  per  cent  or  as  much  as  20 
per  cent  of  soap  and  from  10  to  60  per  cent  of  water. 

Scouring  Soaps.  —  Scouring  soaps  and  scouring  powders 
usually  contain  10  to  20  per  cent  of  soap,  with  80  to  90  per 
cent  of  abrasive  material  —  such  as  fine  sand,  ground  pumice, 
whiting,  or  ground  slate.  Many  also  contain  washing  soda. 
The  quality  of  such  powders  depends  greatly  on  the  fineness 
of  the  abrasive.  Even  a  small  proportion  of  coarse  particles 
may  do  much  damage  by  scratching.  It  is  usually  much 
more  economical  for  the  housekeeper  to  buy  soap,  soda,  and 
abrasives,  such  as  powdered  bath  brick,  whiting,  etc.,  separ- 
ately, and  to  mix  them  for  immediate  use.  It  is  much  easier 
to  judge  of  the  fineness  of  an  abrasive  separately  than  when 
it  is  mixed  with  soap. 


SPECIAL  SOAPS   AND   SCOURING  POWDERS         157 

Experiment  93.  — Test  for  Soda  or  Pearl  Ash  and  Coarse  Abrasives. 

Apparatus: 
Bolting  cloth  sieves. 

Dissolve  as  much  of  the  powdered  material  as  possible  in  alcohol. 
Treat  the  residue  with  hot  water.  Filter.  Acidify  the  nitrate. 
Effervescence  shows  the  presence  of  water-soluble  carbonates  — 
sodium  or  potassium  carbonate. 

Dry  the  residue  from  the  treatment  with  water,  and  sift  it  suc- 
cessively through  bolting  cloths  Nos.  4,  8,  12,  and  16.  The  coarse 
particles  of  abrasive  materials  will  be  left  on  the  sieves.  By  using 
a  weighed  quantity  of  soap  (e.g.  100  grams)  and  weighing  these 
coarse  particles  left  on  the  sieves,  we  may  estimate  the  proportion 
of  coarse  abrasive  in  the  soap. 


CHAPTER  XXX 

SOLUTION  AND  EMULSIFICATION   OF  FATS.      THE 
CLEANING   OF  FABRICS 

Experiment  94. 

Materials : 

Cottonseed  oil  or  olive  oil,  lard,  and  the  liquids  enumerated 

below. 

Caution.  —  Perform  this  experiment  in  a  room  in  which  no 
flames  are  burning. 

Put  the  oil  into  8  test  tubes,  to  the  depth  of  |  inch.  Cover, 
respectively,  to  the  depth  of  i  inch,  with  the  following  liquids, 
shake,  and  allow  to  settle :  (i)  Ether,  (2)  Benzene  (from  coal  tar), 

(3)  Benzine  (from  petroleum.     Note  the  difference  in  spelling), 

(4)  Gasoline,   (5)   Kerosene,   (6)   Chloroform,   (7)   Carbon  tetra- 
chloride,  (8)  Turpentine. 

Put  a  little  lard  into  a  beaker  or  evaporating  dish,  add  one  of 
the  more  volatile  of  the  above  liquids,  e.g.  benzine  or  benzene, 
and  stir  for  a  minute  or  two.  If  the  lard  does  not  all  dissolve, 
filter  through  a  dry  filter  on  to  a  watch  glass,  allow  to  evaporate 
in  a  warm  place,  and  test  the  residue  either  by  putting  it  in  a  cool 
place  to  see  if  it  will  solidify,  or  by  stirring  it  with  a  little  Sudan 
III  solution,  washing  off  with  alcohol  and  adding  hot  water.  (See 
Experiment  85,  p.  149.) 

Experiment  95. 

Materials : 

Cottonseed  or  olive  oil. 
Lard. 

Soap  solution. 
Wood  alcohol. 

Albumin  solution  (made  either  by  mixing  white  of  egg  with 

an  equal  volume  of  water  and  beating  with  an  egg  beater, 

or  by  dissolving  dry  egg  albumin  in  water). 

Put  the  oil  into  7  test  tubes  to  the  depth  of  \  inch.     Cover  with 

the  following  liquids  to  the  depth  of  i  inch,  shake,  and  allow  to 

settle :  (i)  Water,  (2)  Alcohol,  (3)  Wood  alcohol,  (4)  Soap  solu- 

158 


SOLUTION  AND   EMULSIFICATION  OF  FATS        159 

tion,  (5)  Sodium  carbonate  solution,  (6)  Albumin  solution, 
(7)  Albumin  solution  to  which  a  few  drops  of  sodium  carbonate 
have  been  added. 

What  general  difference  do  you  observe  between  the  behavior 
of  these  liquids  towards  the  oil  and  that  of  the  liquids  used  in 
Experiment  94?  What  differences  do  you  observe  between  the 
behavior  of  liquids  1,2,  and  3,  and  that  of  liquids  4,  5,  and  7  of 
the  present  experiment? 

Shake  lard  with  cold  soap  solution  and  with  hot  soap  solution. 
In  which  instance  does  it  behave  like  the  oil? 

When  a  fat  or  oil  dissolves  in  ether,  gasoline,  benzine  (a 
petroleum  product)  or  benzene  (a  coal-tar  product),  the 
product  is  a  clear,  homogeneous  liquid,  similar  to  that  ob- 
tained by  dissolving  salt,  sugar,  or  alcohol  in  water.  This 
clear  liquid  is  a  solution.  Liquid  fats  (oils)  shaken  with 
water,  in  which  they  are  insoluble,  break  up  into  fine  globules 
which  are  distributed  through  the  water  and  impart  to  it  a 
turbid  appearance.  This  turbid  suspension  of  oil  in  water 
rapidly  separates  into  two  clear  layers,  the  lower  one  being 
water,  the  upper  one  oil.  There  are,  however,  certain  sub- 
stances which  when  dissolved  in  water  render  it  capable  of 
holding  the  minute  droplets  of  oil  in  more  permanent  sus- 
pension. Such  a  permanent  or  persistent  suspension  of  oil 
in  water  is  termed  an  emulsion.  Soap  is  one  of  the  best 
emulsifying  agents.  Washing  soda  and  caustic  soda  have  a 
similar  effect  —  due  to  the  formation  of  a  certain  amount  of 
soap  by  their  action  upon  the  fatty  acids  always  present  in 
small  quantities  in  natural  oils. 

The  detergent  effect  of  soap  is  due  to  its  emulsifying  prop- 
erties. Those  constituents  of  the  dirt  on  soiled  or  spotted 
clothing  which  are  not  soluble  in  water  are,  as  a  rule,  of  a 
fatty  nature.  The  addition  of  soap  or  soda  to  the  water 
renders  it  capable  of  emulsifying  the  fats  into  fine  droplets, 
which  are  then  carried  out  of  the  fabric.  The  removal  of 
the  fat  loosens  any  other  dirt  (earthy  matter,  etc.)  which 
was  held  in  position  by  the  fat. 


160  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

A  number  of  plant  and  animal  substances  are  known 
which  have  decided  emulsifying  power,  and  some  of  these 
have  found  use  in  household  practice.  Examples  are  ox 
gall  (i.e.  bile),  soapbark,  and  soapwort. 

The  Cleaning  of  Fabrics 

Stains  on  clothing  commonly  consist  of  a  solid  or  sirupy 
substance  holding  miscellaneous  particles  of  dirt. 

Numerous  devices  are  used  practically  for  the  removal 
of  such  stains,  but  all  of  these  are  directed  towards  the  re- 
moval of  the  dirt-retaining  agent.  If  this  is  of  the  nature 
of  a  sugar,  starch,  or  gum,  hot  water  will  remove  the  stain. 
Stains  based  on  fats  are,  however,  more  troublesome.  A  fat 
may  be  removed:  (i)  By  melting  and  absorption,  (2)  by 
solution,  and  (3)  by  emulsification.  Blotting  paper,  Fuller's 
earth,  French  chalk,  and  pipe  clay  are  among  the  best  sub- 
stances used  to  absorb  fats.  A  hot  iron  is  used  with  the 
blotting  paper  or  other  absorbent  to  melt  solid  fats  and  to 
make  liquid  ones  flow  more  readily.  They  flow  away  from 
the  hot  iron  into  the  absorbent,  which  is  placed  beneath  the 
cloth. 

Dry  cleaning  practice  depends  upon  the  solvent  action  of 
the  liquids  used.  Of  the  solvents  enumerated  in  the  direc- 
tions for  Experiment  94,  only  those  can  be  used  which  evapo- 
rate quickly,  so  as  to  leave  the  cloth  dry  and  free  from  dis- 
agreeable odor.  Kerosene  and  turpentine  are  not  sufficiently 
volatile  for  the  purpose.  Of  the  more  volatile  solvents, 
ether,  benzene,  benzine,  and  gasoline  form  explosive  mix- 
tures with  air,  and  are  therefore  not  suitable  for  use  in  the 
same  room  with  a  stove,  lamp,  or  flame  of  any  kind.  Ether 
and  chloroform  are  objectionable  on  account  of  their  anaes- 
thetic action.  Carbon  tetrachloride  is  the  safest  solvent 
to  use,  being  non-inflammable  and  having  only  slight  physio- 
logical effect.  But  the  petroleum  products,  benzine  and 


SOLUTION  AND  EMULSIFI  CATION  OF  FATS        161 

gasoline,  are  much  cheaper,  and  are  therefore  frequently 
used.  The  disagreeable  odor  of  benzine  can  be  partially 
removed  by  shaking  it  with  charcoal  and  then  filtering  — 
a  process  easily  carried  on  in  the  household.  A  more  effective 
method  is  to  shake  it  with  sodium  plumbite  (Na2PbC>2)  and 
redistill  it.  The  odor  is  also  sometimes  masked  by  the  addi- 
tion of  oil  of  sassafras. 

Since  grease  spots  frequently  contain  other  substances 
than  fats,  a  mixture  of  solvents  may  be  more  efficient  than 
a  single  liquid.  Mixtures  of  alcohol  with  one  or  more  of  the 
fat  solvents  are  sometimes  used,  e.g.  i  drachm  each  of  ether, 
chloroform,  and  alcohol  are  mixed  with  i  quart  of  deodorized 
benzine. 

Common  laundry  practice  is  based  largely  upon  the  prin- 
ciple of  emulsification,  soap  being  the  emulsifying  agent.  The 
use  of  hot  water  not  only  melts  the  fats,  but  assists  the  emulsi- 
fication. Sometimes  the  action  of  the  soap  is  supplemented 
by  that  of  a  fat  solvent,  such  as  carbon  tetrachloride,  paraffin 
wax,  kerosene,  naphtha.  (See  Chapter  XXVIII.)  These 
liquids,  although  not  miscible  with  water,  are  emulsified 
by  the  soap  solution.  A  very  good  combination  of  emulsify- 
ing and  solvent  agents  for  fats  is  a  mixture  of  carbon  tetra- 
chloride with  "  Turkey-red  oil."  The  latter  is  a  substance, 
made  by  the  action  of  sulphuric  acid  on  castor  oil,  which 
dissolves  in  water,  yielding  a  solution  somewhat  similar 
to  that  of  soap.  The  mixture  of  Turkey-red  oil  and  carbon 
tetrachloride  is  a  clear  liquid,  which  is  readily  miscible  with 
water  and  which,  like  soap,  renders  the  water  capable  of 
emulsifying  fats.  It  may  be  used  as  a  partial  or  total  sub- 
stitute for  soap  in  the  laundry,  and  also  for  the  removal  of 
stains  by  the  use  of  cold  water.  In  cold  water  it  is  also  excel- 
lent for  the  removal  of  grease  from  the  hands. 


M 


CHAPTER  XXXI 
THE   GENERAL   COMPOSITION   OF  FOODS 

HUMAN  foods  —  and  the  foods  of  animals  in  general  — 
are  complex  mixtures  of  a  large  number  of  substances.  The 
most  important  of  these  substances  may  be  divided  into  two 
great  classes,  viz. : 

I.   The  Inorganic  Foodstuffs. 

1.  Water. 

2.  "  Mineral  matter  "  or  "  ash." 
II.   The  Organic  Foodstuffs. 

1.  Fats. 

2.  Carbohydrates. 

3.  Proteins. 

The  organic  foodstuffs  are  compounds  which  contain 
the  element  carbon;  the  inorganic  foodstuffs  are  those 
which  do  not  contain  carbon.  The  organic  foodstuffs  can 
be  burned ;  the  inorganic  are  incombustible. 

The  Inorganic  Foodstuffs 

Water  is  not  only  taken  as  a  separate  article  of  diet,  and 
as  the  chief  constituent  of  all  beverages,  but  is  also  present 
in  great  abundance  in  some  classes  of  solid  foods,  especially 
in  fresh  fruits,  fresh  vegetables,  and  fresh  meats.  Even 
many  foods  which  are  apparently  dry  contain  very  material 
quantities  of  water.  Wheat  flour,  for  example,  contains 
about  12  per  cent  of  water,  and  bread  about  35  per  cent. 
The  amount  of  water  in  a  food  is  determined  (i.e.  measured) 
by  weighing  the  food,  heating  it  to  the  boiling  point  of  water 
until  it  ceases  to  lose  weight,  and  then  weighing  the  dried 
residue.  The  loss  in  weight  represents  the  water  which  has 
been  driven  off.  The  weight  of  the  residue  represents  the 

162 


THE   GENERAL   COMPOSITION  OF   FOODS          163 

combined  weight  of  the  organic  foodstuffs  and  the  mineral 
matter. 

Experiment  96. 

Materials : 

Potato,  turnip,  or  apple. 
Apparatus : 

Scales  and  weights. 
Water  bath. 

Cut  a  slice  of  potato,  turnip,  or  apple  weighing  about  25  grams. 
Immediately  weigh  it  accurately.  Cut  up  into  fine,  very  thin 
pieces,  place  in  a  weighed  dish,  and  dry  on  the  water  bath  for 
several  hours.  Allow  to  cool  in  a  dry  atmosphere,  and  weigh  the 
residue.  Heat  again  on  the  water  bath  for  an  hour,  allow  to  cool, 
and  weigh.  If  the  weight  has  not  changed  in  the  second  weighing, 
the  drying  is  completed.  Deduct  the  weight  of  the  dish,  and  cal- 
culate the  percentage  of  moisture  the  vegetable  or  fruit  contains. 

EXERCISE 

Consult  the  tables  of  food  composition  in  Appendix  A,  and 
arrange  the  following  foods  in  order  of  their  water  content,  be- 
ginning with  the  driest. 

1.  Bananas  12.  Walnuts 

2.  Apples  13.  Beef,  hindquarter 

3.  Grapes  14.  Salmon 

4.  Watermelons  15.  Whole  milk 

5.  Green  cucumbers  16.  Cream 

6.  Tomatoes  17.  Butter 

7.  Potatoes  1 8.  White  of  eggs 

8.  Cabbage  19.  Yolk  of  eggs 

9.  Oatmeal  20.  Oysters 

10.  Flour  21.   Apple  pie 

11.  Bread  22.  Doughnuts 

When  a  food  is  thoroughly  dried,  the  water  all  passes  off 
as  water  vapor  (steam).  When  the  dried  residue  is  strongly 
heated  in  the  air,  the  organic  foodstuffs  are  burned  and  pass 
off  as  gases  and  the  inorganic  salts  remain  behind  in  the  ash. 
It  must  not  be  thought,  however,  that  the  ash  consists  en- 
tirely of  salts  which  were  present  as  such  in  the  food.  The 


1 64  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

sulphur,  phosphorus,  and  chlorine,  and  the  potassium,  so- 
dium, calcium,  and  magnesium,  which  exist  in  the  ash  as 
sulphates,  phosphates,  and  chlorides,  may  have  been  con- 
stituents of  organic  compounds  in  the  unburned  material. 
And  the  carbon  which  exists  in  the  ash  as  a  constituent  of 
carbonates  must  have  come  either  from  the  salts  of  organic 
acids  or  from  more  complex  organic  compounds,  such  as 
fats,  carbohydrates,  and  proteins. 

Nevertheless,  the  weight  of  the  ash  is  regarded  as  a  rough 
measure  of  the  quantity  of  mineral  matter  in  the  food. 
The  ash  contains  all  the  potassium,  sodium,  calcium,  and 
magnesium  and  iron  of  the  food.  Part  of  the  chlorine,  sul- 
phur, and  phosphorus,  however,  may  pass  off  as  gases  during 
the  combustion  of  the  food. 

Except  in  foods  which  have  been  salted,  the  ash  seldom 
amounts  to  five  per  cent  of  the  weight  of  the  food.  In  many 
foods  it  amounts  to  less  than  one  per  cent. 

The  Organic  Foodstuffs 

The  nature  of  fats  has  already  been  discussed  in  connection 
with  the  manufacture  of  soaps  and  the  removal  of  dirt  from 
fabrics  (Chapters  XXV,  XXVI,  and  XXX).  Sugar  and 
starch  are  typical  carbohydrates.  The  white  of  egg,  the 
lean  of  meat  (muscle  fibers),  and  the  gluten  of  flour  are  ex- 
amples of  proteins. 

It  should  be  noted  that  while  both  fat^s  and  carbohydrates 
are  composed  of  carbon,  hydrogen,  and  oxygen,  the  propor- 
tion of  carbon  is  much  greater,  and  the  proportion  of  oxygen 
much  smaller  in  the  former  class  of  substances  than  in  the 
latter. 

Proteins  differ  from  fats  and  carbohydrates  in  containing 
a  fairly  large  proportion  of  nitrogen  and  a  small  proportion 
of  sulphur,  in  addition  to  carbon,  hydrogen,  and  oxygen. 
Besides  these  five  elements  a  number  of  proteins  contain  a 


THE   GENERAL   COMPOSITION  OF  FOODS 


small  proportion  of  phosphorus.    A  few  also  contain  iron 
or  other  elements. 

The  average  composition  of  the  three  great  classes  of  or- 
ganic nutrients  is  given  in  the  following  table : 

AVERAGE   ELEMENTARY  COMPOSITION   OF  NUTRIENTS 


FATS 

CARBOHYDRATES 

PROTEINS 

Carbon. 

Per  Cent 

76  S 

Per  Cent 

A  A    A 

Per  Cent 
r  -2 

Hydrogen      

I2.O 

6.2 

7 

Oxv£6n 

II.  C 

4.Q  4- 

22 

16 

Sulphur                    .... 

i 

The  percentage  of  hydrogen  in  proteins  does  not  differ 
greatly  from  that  in  carbohydrates.  In  carbon  and  in 
oxygen  content,  the  proteins  are  intermediate  between  the 
fats  and  the  carbohydrates. 


CHAPTER  XXXII 
THE   CARBOHYDRATES.     I 

BEFORE  taking  up  the  consideration  of  the  functions  of  the 
various  classes  of  foodstuffs  it  is  desirable  that  we  should 
learn  something  about  the  chemical  constitution  and  be- 
havior of  the  carbohydrates  and  proteins,  similar  to  what 
we  have  already  learned  about  the  fats. 

Carbohydrates  (literally,  hydrates  of  carbon)  take  their 
class  name  from  the  circumstance  that  in  combination  with 
carbon  they  contain  the  elements  of  water  in  the  same  pro- 
portion as  water  itself.  Examples  are  glucose,  C6Hi2O6; 
cane  sugar,  Ci2H22On;  starch,  (C&HioOsV  But  the  name 
does  not  adequately  describe  the  class ;  for,  on  the  one  hand, 
many  compounds  which  are  not  carbohydrates  (e.g.  form- 
aldehyde, CH2O ;  acetic  acid,  CjjILA ;  lactic  acid,  C3H6O3) 
contain  hydrogen  and  oxygen  in  this  proportion  combined 
with  carbon ;  and  on  the  other  hand  there  are  a  few  rare 
carbohydrates  whose  molecules  have  more  than  twice  as 
many  hydrogen  atoms  as  oxygen  atoms. 

The  simplest  carbohydrates  are  called  monosaccharides. 
These  are  sweet-tasting  substances,  which  are  so  abundantly 
soluble  in  water  as  to  form  sirups  with  it.  In  short,  they 
are  sugars.  Honey  is  a  sirup  of  two  monosaccharides,  called 
glucose  (or  dextrose}  and  fructose  (or  levulose),  together  with 
a  small  proportion  (less  than  10  per  cent)  of  that  sugar 
(cane  sugar)  which  is  most  familiar  to  us  —  and  which  is  not 
a  monosaccharide.  (See  beyond.) 

Now,  the  term  carbohydrates  embraces  the  monosac- 
charides and  all  substances  which  by  hydrolysis  are  converted 
into  monosaccharides. 

Monosaccharides  are  divided  into  two  classes  —  aldoses  and 
ketoses  —  according  to  their  structural  formulas,  and  into  several 

166 


THE   CARBOHYDRATES  167 

classes  —  pentoses,  hexoses,  etc.  —  according  to  the  number  of 
carbon  atoms  they  contain.  Glucose  and  fructose  are  both 
hexoses,  having  the  molecular  formula,  C6H12O6.  Structurally, 
glucose  is  an  aldose,  fructose  a  ketose.  Aldoses  contain  the  radicle 
or  "  group  "  of  atoms  : 


which  is  common  to  a  class  of  compounds  called  aldehydes,  of 
which  the  disinfectant,  Jormaldehyde, 

/H 

H—  C=O 

and  the  flavoring  matter,  benzaldehyde  (oil  of  bitter  almonds), 
C6H5— 


are  familiar  examples. 

Ketoses  contain  the  group  =C=O,  joined  to  two  other  car- 
bon atoms,  and  belong  to  a  class  of  compounds  called  ketones. 
Acetone, 


a  product  of  the  dry  distillation  of  wood,  is  the  simplest  represent- 
ative of  the  ketones. 

The  structural  formulas  of  glucose  and  fructose  are  : 
H  H 

I  I 

H—  C—  OH  H—  C—  OH 

I  I 

H—  C—  OH  H—  C—  OH 

I  I 

H—  C—  OH  H—  C—  OH 

I  I 

HO—  C  —  H  HO—  C—  H 


H—  C—  OH 

-H  | 

H—  C—  OH 


c 


V 

H 

Glucose  (Dextrose)  Fructose  (Levulose) 


1 68  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

It  is  clear  from  these  formulas  that  these  monosaccharides, 
in  addition  to  being  aldehydes  or  ketones,  are  also  alcohols 
containing  several  — OH  groups.  And  this  alcoholic  con- 
stitution appears  to  be  true  of  all  the  carbohydrates,  however 
complex  their  molecules. 

Carbohydrates  may  be  classified  as  follows : 

I.  Sugars.  —  These  form  crystals  and  dissolve  in  water. 
In  solution  they  will  pass  through  membranes  of  parchment 
paper.     They  have  a  sweet  taste. 

The  most  important  sugars  are: 

(1)  The  monosaccharides — glucose,  fructose  and  galac- 

tose. 

(2)  The  disaccharides  —  maltose,  lactose,  and  sucrose. 

II.  Polysaccharides.  —  This    class    includes    dextrin    and 
some  other  gums,  pectin,  starch,  glycogen,  and  cellulose.     Dex- 
trin, pectin,  and  glycogen  are  soluble  in  water,  but  do  not 
pass  through  parchment  paper  with  the  water.     Starch  is 
insoluble  in  cold  water  and  cellulose  insoluble  even  in  hot 
water. 

Experiment  97. 

Materials : 

Monosaccharides : 

Glucose  (dextrose,  grape  sugar). 
Fructose  (levulose,  fruit  sugar). 
Disaccharides : 

Maltose  (malt  sugar). 
Lactose  (milk  sugar) . 
Sucrose  (saccharose,  cane  sugar). 
Polysaccharides : 
Dextrin. 
Starch. 

Cellulose  (absorbent  cotton  or  filter  paper). 
Taste  the  carbohydrates.     The  sweet  ones  are  sugars.    Which 
of  the  above  classes  are  included  under  this  term? 

Test  the  solubility  of  the  carbohydrates  in  cold  water  by  shak- 
ing about  |  gram  of  each  with  half  a  test  tube  of  water.  Which 
of  them  are  insoluble  in  cold  water?  Which  one  of  the  sugars  is 


THE   CARBOHYDRATES  169 

much  less  soluble  than  the  others?  How  does  this  one  compare 
with  the  others  in  sweetness  ?  Keep  the  solutions  for  subsequent 
experiments. 

Find  out  whether  any  of  the  carbohydrates  insoluble  in  cold 
water  is  soluble  in  hot  water.  Keep  the  solutions. 

Experiment  98.  —  Fehling's  Solution,  Fehling-Benedict  Solution, 
and  the  Meaning  of  "  Reduction." 

Materials  : 

Cuprous  oxide,  Cu2O,  and  Cupric  oxide,  CuO. 
Solutions  of : 

Copper  sulphate,  17.3  grams  to  i  liter. 
Sodium  potassium  tartrate  (Rochelle  salt),  346  grams  to 

i  liter. 
Sodium  citrate,  173  grams  to  i  liter. 

(a)  Note  the  colors  of  the  two  oxides  of  copper.     Which  of  the 
two  contains  the  larger  proportion  of  oxygen  ?     (See  p.  39.) 

To  "  reduce  "  a  compound  is  to  take  away  oxygen  from  it. 
Which  of  the  oxides  of  copper  can  be  changed  into  the  other  by 
reduction  ? 

(b)  Dissolve  a  little  of  the  cupric  oxide  in  dilute  sulphuric  acid. 
What  salt  is  present  in  the  solution  so  prepared  ?     Write  equation 
for  its  formation.     We  may  regard  this  salt  as  containing  cupric 
oxide,  CuO,  combined  with  SO3,  the  anhydride  of  sulphuric  acid. 

Acid  anhydrides  are  the  oxides  which  bear  to  acids  the  same 
relation  that  the  basic  oxides  bear  to  the  bases ;  i.e. : 

Anhydride  +  Water  =  Acid 

Thus,  carbon  dioxide,  CO2,  is  the  anhydride  of  carbonic  acid, 
H2CO3;  sulphur  dioxide,  SO2,  the  anhydride  of  sulphurous  acid, 
H2S03,  etc. 

(c)  Add  to  a  little  of  the  solution  prepared  in  (b)  a  little  more 
than  enough  sodium  hydroxide  solution  to  neutralize  the  acid. 
What  is  the  precipitate?    Add  more  sodium  hydroxide  and  boil. 
What  is  formed?     (Compare  Expt.  49.) 

(d)  To  copper  sulphate  solution  add,  first,  Rochelle  salt  solu- 
tion, and  then  sodium  hydroxide.     What  effect  has  the  Rochelle 
salt  on  the  reaction  between  sodium  hydroxide  and  copper  sul- 
phate ?     We  may  regard  the  resulting  solution  (Fehling's  solution) 
as  containing  cupric  oxide,  CuO. 

(e)  Make  the  same  experiment  as  (d),  using  sodium  citrate  in- 
stead of  Rochelle  salt. 


1 70  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

(/)  To  copper  sulphate  solution  add  sodium  carbonate  solution. 
What  is  the  precipitate  ?  Can  it  be  regarded  as  containing  cupric 
oxide? 

(g)  To  copper  sulphate  solution  add,  first,  sodium  citrate,  then 
sodium  carbonate.  The  product  is  Fehling-Benedict  solution, 
which  keeps  better  than  Fehling's  solution.  Can  Fehling-Benedict 
solution  also  be  regarded  as  containing  cupric  oxide? 

When  Fehling's  or  Fehling-Benedict  solution  is  reduced, 
cuprous  oxide  is  formed.  This  oxide  is  not  capable  of  forming 
soluble  compounds  with  tartrates  and  citrates  similar  to  those 
formed  by  cupric  oxide,  and  is  therefore  precipitated.  The 
precipitate  obtained  is,  however,  not  always  red,  but  often, 
especially  with  the  Fehling-Benedict  reagent,  yellow  or  green, 
probably  due  to  the  presence  of  more  or  less  cuprous  hydroxide. 

Experiment  99. 

Materials : 

The  solutions  of  sugars  prepared  in  Experiment  97. 

To  separate  5  cc.  portions  of  Fehling-Benedict  solution  add  a 
few  drops  of  the  sugar  solutions.  Boil  for  a  minute  or  two.  What 
is  the  precipitate?  Which  of  the  sugars  produce  it?  These  are 
called  "  reducing  sugars."  What  sugar  is  not  a  reducing  sugar? 

Experiment  100. 

Materials : 

Sucrose  solution  prepared  in  Experiment  97. 

To  the  sucrose  solution  add  a  little  concentrated  hydrochloric 
acid.  Boil  for  a  minute  or  two.  Cool.  Put  in  a  small  piece  of 
litmus  paper  and  add  sodium  hydroxide  little  by  little  until  the 
acid  is  neutralized.  Add  a  little  of  the  neutralized  solution  to 
about  5  cc.  Fehling-Benedict  solution,  and  boil. 

Does  unchanged  sucrose  affect  Fehling-Benedict  solution? 
What  change  must  have  been  caused  by  boiling  the  sucrose  with 
the  hydrochloric  acid? 

Experiment  101. 

Material : 
Starch. 

Absorbent  cotton  (cellulose). 
Sodium  carbonate  powdered  (soda  ash). 


THE   CARBOHYDRATES  171 

(a)  In  a  beaker  or  dish  mix  a  little  starch  (J  to  f  gram)  with  a 
teaspoonful  of  water.     Heat  about  50  cc.  of  water  in  a  dish  to 
boiling,  and  add  the  mixture  of  starch  and  cold  water.     Boil  for 
a  minute  or  two,  stirring  constantly. 

(b)  Pour  off  some  of  the  solution  into  a  test  tube  and  cool  it 
under  the  tap.     To  a  small  portion  of  the  cold  solution  add  a  little 
iodine  solution.     Warm  the  solution  and  cool  it  again.     Does 
iodine  color  hot  starch  solution? 

(c)  To  another  portion  of  the  cold  solution  add  a  few  drops  of 
Concentrated  sulphuric   acid.     Boil  until  a  drop  of  the  liquid 
poured  off  into  cold  iodine  solution  no  longer  colors  the  latter. 
This  is  evidence  that  starch  is  no  longer  present.     Pour  off  the 
main  portion  of  the  boiled  solution  into  a  beaker  and  add  powdered 
sodium  carbonate,  little  by  little,  until  the  acid  is  neutralized. 
Add  a  little  of  this  neutralized  solution  to  Fehling-Benedict  solu- 
tion in  a  test  tube,  and  boil  for  a  minute. 

What  do  you  infer  as  to  the  effect  of  boiling  the  starch  with  the 
acid? 

(d)  Put  a  little  absorbent  cotton  into  a  test  tube,  cover  it  with 
concentrated  sulphuric  acid,  and  allow  to  stand  a  minute  or  two. 
Note  whether  the  cellulose  dissolves  in  the  sulphuric  acid.     Pour 
off  into  five  or  six  times  its  volume  of  cold  water  and  boil  for  two  or 
three  minutes.     Neutralize  the  acid  (in  a  beaker)  with  sodium 
carbonate  as  in  (c),  add  to  Fehling-Benedict  solution,  and  boil. 

It  is  evident  from  the  above  experiments  that  reducing 
sugars  can  be  formed  from  cane  sugar,  starch,  and  cellulose 
by  boiling  with  acids.  The  acid  is,  however,  not  used  up  in 
the  reaction,  which  is  really  one  between  the  carbohydrates 
and  water  —  in  other  words,  a  hydrolysis.  The  acid  is  merely 
a  catalytic  agent,  promoting  the  hydrolysis. 

The  final  products  of  hydrolysis  of  all  the  higher  carbohy- 
drates (disaccharides  and  polysaccharides)  are  monosac- 
charides.  Each  disaccharide  molecule  hydrolyzes  into  two 
monosaccharide  molecules,  and  each  polysaccharide  molecule 
into  several  monosaccharide  molecules.  The  relations  of  the 
more  familiar  higher  carbohydrates  to  the  monosaccharides 
are  as  follows : 


172  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

i.  Disaccharides: 

Sucrose  +  Water  =  Glucose  +  Fructose 
Lactose  +  Water  =  Glucose  +  Galactose 
Maltose  +  Water  =  Glucose  +  Glucose 

All  three  of  these  reactions  are  expressed  by  the  equation : 
Ci2H22On  +  H2O 


2.  Polysaccharides : 

Dextrin  +  Water  =  Glucose 

Starch  +  Water  =  Glucose 

Glycogen  +  Water  =  Glucose 

Cellulose  +  Water  =  Glucose 

All  of  these  reactions  correspond  to  the  equation : 
(C6H1005)n  +  n  H20  =  n  C6H12O6 

in  which  n  stands  for  an  unknown  number. 


CHAPTER  XXXIII 
THE   CARBOHYDRATES.     II 

Description  of  the  Monosaccharides,  C6Hi2O6 

Glucose,  also  called  dextrose  and  grape  sugar,  occurs  very 
widely  distributed  in  plant  juices,  and  also  in  smaller  pro- 
portions in  the  blood  of  animals.  It  is  a  prominent  constitu- 
ent of  honey  and  of  raisins,  and  sometimes  separates  from 
these  in  the  solid  form.  It  does  not  crystallize  nearly  as 
readily  as  sucrose  (cane  sugar),  however,  and  in  the  processes 
used  to  separate  the  latter  from  the  juice  of  the  sugar  cane  and 
from  the  juice  of  the  sugar  beet,  the  glucose  remains  in  the 
molasses.  It  is  less  sweet  than  sucrose. 

Commercial  glucose,  which  appears  on  the  market  both 
in  solid  form  and  in  a  sirup,  is  manufactured  by  hydrolysis 
of  starch  by  an  acid.  In  addition  to  glucose  proper,  com- 
mercial glucose  contains  the  polysaccharide  dextrin,  and  the 
disaccharide  maltose,  —  these  being  also  formed  by  the  hy- 
drolysis of  starch.  Commercial  glucose  is  cheaper  than  cane 
sugar,  and  is  sometimes  used  as  a  substitute  for,  or  as  an 
adulterant  of,  the  latter.  It  is  also  "  compounded  "  (i.e. 
mixed)  with  cane  sirup  to  form  a  table  sirup  known  as 
"  corn  sirup." 

Fructose,  also  called  levulose  (or  laevulose)  and  fruit 
sugar,  is  found  associated  with  glucose  in  fruit  juices  and  in 
honey.  A  mixture  of  equal  quantities  of  glucose  and  fruc- 
tose is  produced  when  cane  sugar  is  hydrolyzed. 

In  the  preparation  of  jams  and  preserves  much  of  the 
cane  sugar  put  in  is  hydrolyzed  by  the  acids  of  the  fruit, 
and  the  jam  and  preserves  contain  this  mixture  of  glucose 

173 


174  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

and  fructose.  The  hydrolysis  of  sucrose  is  technically  spoken 
of  as  the  inversion  of  sugar,  and  the  mixture  of  equal  quanti- 
ties of  glucose  and  fructose  as  invert  sugar. 

The  term  "  inversion  "  refers  to  an  effect  which  sugar  solutions 
have  upon  so-called  "  plane-polarized  "  light.  In  terms  of  the 
wave  theory  of  light,  plane-polarized  light  has  all  its  vibrations  in 
one  plane  at  right  angles  to  the  direction  of  the  ray,  while  ordinary 
light  has  vibrations  in  all  directions  at  right  angles  to  the  direction 
of  the  ray.  The  instrument  used  to  measure  the  effect  of  sub- 
stances upon  polarized  light  is  called  a  polariscope  or  polar  im- 
eter.  It  consists  essentially  of  two  prisms  of  calcite  (crystallized 
calcium  carbonate)  at  opposite  ends  of  a  tube.  One  prism  is 
fixed  in  position;  the  other  can  be  rotated  about  the  axis  of 
the  tube.  When  light  admitted  through  the  fixed  prism  is  al- 
lowed to  pass  through  air  or  water  to  the  second  prism,  it  only 
passes  completely  in  case  this  second  prism  is  in  a  similar  posi- 
tion to  the  first.  If  the  second  is  rotated  into  a  position  at 
right  angles  to  the  first,  the  light  is  shut  out  entirely.  In  inter- 
mediate positions  it  is  partially  transmitted.  Now,  if  in  passing 
from  prism  to  prism  the  light  passes  through  a  sugar  solution, 
the  second  prism  being  in  a  similar  position  to  the  first,  the  light 
is  no  longer  fully  transmitted  through  the  second  prism.  If, 
however,  this  second  prism  be  rotated  —  it  may  be  to  the  right 
or  it  may  be  to  the  left  —  through  a  certain  angle,  the  light  will 
be  fully  transmitted.  The  angle  through  which  the  prism  has 
to  be  rotated  is  equal  to  the  angle  through  which  the  "  plane  of 
polarization  "  is  rotated  by  the  sugar  solution. 

Now,  sucrose  and  glucose  rotate  the  plane  of  polarization  to 
the  right,  while  fructose  ("  levulose  ")  rotates  it  to  the  left.  At 
room  temperature  fructose  rotates  the  plane  more  to  the  left 
than  an  equal  quantity  of  glucose  rotates  it  to  the  right.  Hence, 
invert  sugar  is  levorotatory,1  and  the  hydrolysis  of  the  sucrose 
changes  a  dextrorotatory  solution  into  a  levorotatory  one. 

Galactose  does  not  occur  as  such,  but  is  produced  by 
hydrolysis  of  lactose  and  of  certain  higher  carbohydrates, 
galactans,  which  bear  to  it  a  similar  relation  to  that  which 
starch  bears  to  glucose. 

1  Latin,  laws  =  left,  dexter  =  right. 


THE   CARBOHYDRATES  175 

Alcoholic  Fermentation 

The  ferment,  zymase,  contained  in  yeast,  causes  the  mono- 
saccharides  to  decompose  into  alcohol  and  carbon  dioxide  : 

=  2  C2H5OH  +  2  CO2 


This  is  the  reaction  which  characterizes  the  fermentation  of 
fruit  juices.  It  is  made  use  of  in  the  manufacture  of  wines 
and  sometimes  occurs  in  jars  of  fruit  which  have  not  been 
thoroughly  sterilized.  The  same  reaction  is  involved  in  the 
final  stage  of  fermentation  of  grains  in  the  manufacture  of 
beer  and  whisky,  and  in  the  raising  of  bread. 


Description  of  the  Disaccharides, 

Sucrose,  also  called  saccharose  and  cane  sugar,  is  of  very 
common  occurrence  in  the  vegetable  world,  being  found  in 
considerable  quantity  in  the  fruits  and  juices  of  many  plants 
—  usually  mixed  with  more  or  less  glucose  and  fructose. 
The  most  important  sources  of  sucrose  are  the  sugar  beet, 
sugar  cane,  sorghum  cane,  and  sugar  maple. 

Pure  sucrose  obtained  from  any  of  these  sources  does  not 
differ  from  that  obtained  from  any  of  the  others.  Rock 
candy  is  chemically  pure  sucrose,  and  commercial  white 
sugar  contains  very  little  impurity. 

The  hydrolysis  (inversion)  of  cane  sugar  can  be  brought 
about  by  boiling  the  aqueous  solution  with  an  acid.  Hence 
this  reaction  takes  place  in  the  preserving  of  fruits.  (See 
above.)  It  can  also  be  accomplished  by  one  or  more  fer- 
ments commonly  called  invertases  or  invertins,  but  more 
correctly  termed  sucrases.  There  is  a  ferment  of  this  class 
in  the  yeast  plant  (which  assists  in  alcoholic  fermentation  by 
converting  sucrose  into  glucose  and  fructose)  and  another 
in  the  intestinal  juice  (which  effects  the  same  change  as  a 
step  in  the  digestion  of  sugar). 


176  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Experiment  102. 

Materials : 
Yeast. 
Cane  sugar. 
Sand. 

Mortar  and  pestle. 

Grind  a  yeast  cake  with  sand  and  a  little  water.  Dilute  to  50  cc., 
add  5  cc.  ether,  and  filter.  To  the  filtrate  add  100  cc.  alcohol. 
This  precipitates  the  sucrase  (invertase).  Filter.  Change  the 
receiver  and  dissolve  the  precipitate  by  pouring  about  20  cc.  water 
through  the  filter. 

Dissolve  about  \  gram  sugar  in  a  half  test  tube  of  water.  Add 
a  little  of  the  sucrase  solution  just  prepared,  and  allow  to  stand 
about  half  an  hour.  Then  add  a  little  of  the  solution  to  Fehling- 
Benedict  solution,  and  boil  for  a  minute  or  two.  If  no  precipitate 
is  formed,  allow  the  sugar  solution  to  stand  another  half  hour  and 
repeat  the  test. 

Cane  sugar  has  no  action  on  Fehling's  solution,  but  invert 
sugar,  of  course,  has.  In  other  words,  cane  sugar  is  non- 
reducing,  but  yields  reducing  sugars  upon  hydrolysis. 

Maltose,  or  malt  sugar,  yields  only  a  single  kind  of  monosac- 
charide  —  one  molecule  of  maltose  hydrolyzing  to  two  mole- 
cules of  glucose.  This  hydrolysis  is  readily  effected  by  boiling 
the  maltose  with  dilute  strong  acids.  It  is  also  brought 
about  by  the  action  of  ferments,  called  maltases,  one  of  which 
is  a  constituent  of  the  intestinal  juice.  Maltose  is  formed 
from  starch  by  the  action  of  amylolytic  (i.e.  starch-hydro- 
lyzing)  ferments,  amylases.  An  amylase  known  as  diastase 
is  developed  in  germinating  grain  and  hence  is  present  in 
malt,  malt  extract,  and  beerwort.  Two  amylases  are  con- 
cerned in  digestion  of  starch.  These  are  the  ptyalin  of  the 
saliva  and  the  amylopsin  of  the  pancreatic  juice.  Maltose 
is  also  formed  as  an  intermediate  product  when  starch  is 
hydrolyzed  by  boiling  with  acid,  as  in  the  manufacture  of 
commercial  glucose. 

Lactose  —  milk  sugar  or  sugar  of  milk  —  hydrolyzes  to 
glucose  and  galactose.  It  occurs  in  the  milk  of  mammals. 


THE   CARBOHYDRATES  1 77 

Fresh  cow's  milk  contains  about  five  per  cent.  Lactose 
is  much  less  soluble  in  water  than  the  other  sugars,  and 
has  only  a  slightly  sweet  taste.  It  is  commonly  used  in 
pharmacy  as  a  "  base  "  (or  diluent)  for  pills  and  tablets. 
In  digestion  lactose  is  hydrolyzed  in  the  intestine  under  the 
influence  of  a  ferment  known  as  lactase.  Lactose  is  con- 
verted into  lactic  acid  by  a  certain  class  of  bacteria  which  are 
normally  present  in  fresh  milk  and  are  very  abundant  in 
buttermilk.  The  souring  of  milk  is  due  to  this  fermentation. 
Maltose  and  lactose  reduce  Fehling's  solution. 

The  Polysaccharides  (C6H10O5)n 

Starch  is  the  principal  form  of  digestible  carbohydrate 
in  cereal  grains  and  their  products  and  in  potatoes.  It 
constitutes  more  than  half  the  solid  matter  of  all  the  common 
cereals  and  about  three  fourths  of  that  of  the  potato.  Being 
the  principal  storage  form  of  carbohydrates  in  most  green 
plants,  starch  is  found  in  more  or  less  abundance  in  almost 
all  vegetable  foods.  For  commercial  purposes  starch  is 
isolated  from  wheat,  maize  (corn),  rice,  and  potatoes.  Arrow- 
root, tapioca,  and  sago  are  also  almost  pure  starch.  All  these 
commercial  forms  of  starch  contain  water,  about  eighteen 
per  cent  as  an  average.  Starch  granules  of  different  plants 
vary  in  size  and  structure ;  so  the  source  of  a  starch  which  has 
not  been  altered  by  heat,  fermentation,  or  the  action  of  chemi- 
cal reagents  can  be  determined  by  microscopic  examination. 

Experiment  103. 

Materials : 
Cornstarch. 
Potato  starch. 
Wheat  starch. 
Apparatus : 

Compound  microscope. 
Slides. 

Cover  glasses. 
Medicine  dropper. 


178  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Prepare  the  three  starches  for  microscopic  examination  by  first 
sifting  through  a  60-  or  8o-mesh  sieve,  then  placing  a  small  portion 
on  a  slide  by  means  of  a  knife  point,  adding  a  drop  of  distilled 
water,  putting  on  the  cover  glass  obliquely  (so  as  to  avoid  in- 
closing air  bubbles)  and  then  rubbing  out  the  material  under  the 
cover  glass  between  the  thumb  and  finger  to  separate  the  particles 
and  distribute  them  evenly. 

Examine  the  starches  under  the  microscope,  using  a  magnifica- 
tion of  about  250.  Note  the  general  form  and  comparative  size 
of  the  granules,  and  the  presence  or  absence  of  concentric  ring 
markings  and  of  the  little  depression  called  the  hilum. 

The  granules  of  these  three  starches  are  typical  of  the  three 
general  forms  —  the  circular,  the  irregularly  oval,  and  the  polygonal. 
Note,  however,  that  wheat  starch  consists  of  two  kinds  of  granules 
—  the  larger  having  one  form,  the  smaller  another.  In  the  form 
of  their  granules  rye  and  barley  starches  resemble  wheat  starch; 
arrowroot,  pea,  and  bean  starches  resemble  potato;  and  oats, 
buckwheat,  and  rice  resemble  corn. 

The  most  characteristic  chemical  test  for  starch  is  the  re- 
action with  iodine  in  the  cold.  (See  Expt.  101  (b)  above.) 

When  starch  is  treated  with  hot  water,  the  granules  swell 
and  burst,  and  the  starch  apparently  dissolves  in  the  water, 
forming  an  opalescent  liquid  or  paste.  In  many  respects 
this  liquid  differs  from  the  solutions  of  such  substances  as 
salts,  acids,  bases,  and  sugars.  These  latter  substances, 
which  separate  from  their  solutions  in  crystalline  form,  are 
known  as  crystalloids,  while  starch  is  a  colloid  (literally,  glue- 
like  substance).  When  a  starch  solution  evaporates,  no 
crystals  form,  but  the  starch  gradually  dries  to  a  hard,  horn- 
like or  glue-like  mass,  from  which  it  is  very  difficult  to  drive 
off  the  last  traces  of  water.  An  important  difference  between 
colloids  and  crystalloids  in  solution  will  be  referred  to  later. 
(Chapter  XXXVII.) 

The  hydrolysis  of  starch  by  acids  and  by  amylases  has 
been  referred  to  in  connection  with  glucose  and  maltose. 
On  standing  in  the  cold  with  a  dilute  strong  acid,  starch  is 
converted  into  a  soluble  substance  which  gives  a  blue  color 


THE   CARBOHYDRATES  179 

with  iodine,  and  does  not  reduce  Fehling's  solution.  This 
is  known  as  soluble  starch.  Similar  products  are  formed  by 
the  action  of  organic  acids,  dilute  alkalies,  and  other  reagents. 

Further  hydrolysis  (by  longer  standing  or  by  heating  with 
acid)  produces  soluble  substances  known  as  dextrins,  some 
of  which  give  a  red  coloration  with  iodine,  while  others  give  no 
coloration  at  all.  Commercial  dextrin  is  prepared  by  heating 
starch  for  some  time  to  about  200°  C.  about  (400°  F.)  or  by 
moistening  with  dilute  nitric  or  hydrochloric  acid  and  heat- 
ing to  a  lower  temperature  (100-120°  C.).  In  breadmaking 
some  dextrin  (together  with  maltose)  is  formed  during  the 
rising  by  the  action  of  diastase  on  the  starch  of  the  flour. 
In  the  baking  a  further  portion  of  the  starch  in  the  crust  is 
converted  into  dextrin  by  the  heat.  The  effect  of  toasting 
bread  is  to  convert  some  of  its  starch  into  dextrin.  It  is 
present  in  considerable  abundance  in  some  of  the  malted 
breakfast  foods. 

Dextrin  is  white  when  pure,  but  commonly  yellow  in  com- 
mercial samples.  It  is  soluble  in  water,  giving  a  strongly 
dextrorotatory  solution  (whence  the  name).  The  solution 
is  colloidal,  and  on  drying  behaves  like  that  of  a  starch.  Dex- 
trin is  used  as  a  substitute  for  natural  gums  (some  of  which 
are  analogous  carbohydrates)  in  the  manufacture  of  mucilage, 
label  gums,  and  "  sizes  "  for  giving  a  glazed  finish  to  textiles, 
cardboard,  and  paper.  Dextrin  is  precipitated  from  its 
aqueous  solution  by  the  addition  of  alcohol. 

Glycogen,  sometimes  called  animal  starch,  is  similar  to 
dextrin  in  properties.  It  plays  a  part  in  animal  organisms 
similar  to  that  played  by  starch  in  the  vegetable  world,  — 
the  part  of  a  "  reserve  "  or  "  storage  "  carbohydrate.  It 
is  found  in  the  muscles  and  more  abundantly  in  the  liver,  the 
amount  present  varying  greatly  with  the  condition  of  nutri- 
tion of  the  animal.  Stored  glycogen  is  rapidly  used  up  under 
conditions  of  starvation  and  of  hard  muscular  work.  Gly- 
cogen is  a  white  powder,  soluble  in  water  to  an  opalescent 


l8o  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

colloidal  solution.  With  iodine  it  gives  a  reddish  coloration, 
somewhat  similar  to  that  given  by  dextrin. 

The  celluloses  constitute  the  walls  of  the  cells  of  plants, 
thus  acting  as  a  sort  of  plant  skeleton.  Celluloses  are  in- 
soluble in  water  and  in  dilute  acids  and  alkalies.  The  "  crude 
fiber  "  which  the  analyst  determines  in  foods,  by  successively 
treating  with  dilute  acid  and  alkali,  and  weighing  the  un- 
dissolved  residue,  consists  mainly  of  cellulose.  By  heating 
with  strong  acid,  ordinary  cellulose  —  such  as  that  of  cotton 
and  linen  —  is  hydrolyzed,  yielding  glucose.  Cotton  and 
linen  are  comparatively  pure  cellulose,  and  straw,  wood,  and 
paper  contain  large  proportions  of  this  class  of  carbohydrates. 

The  proportion  of  cellulose  in  different  parts  of  a  plant 
vary  widely.  It  is  usually  most  abundant  in  the  stem,  with 
less  in  the  foliage  and  least  in  the  fruit.  Such  vegetables 
as  celery,  beets,  and  turnips  contain  much  more  cellulose  than 
do  potatoes,  flour,  and  fruits.  As  a  plant  matures,  its  cell 
walls  thicken.  Consequently  the  proportion  of  cellulose 
in  its  stem,  branches,  and  roots  increases,  and  some  of  the 
cellulose  is  converted  into  a  harder  form  called  lignocellulose 
or  woody  tissue.  This  accounts  for  the  toughness  of  over- 
mature vegetables. 

Cellulose  is  digested  to  only  a  slight  extent.  The  foods 
rich  in  cellulose,  e.g.  turnips  and  green  vegetables,  do  not 
contribute  much  to  the  fuel  value  of  the  diet.  As  regulators 
of  physiological  processes,  however,  they  are  of  importance, 
both  on  account  of  the  salts  and  other  ash  constituents  which 
they  contain  and  on  account  of  the  cellulose  which  mechani- 
cally stimulates  the  intestines,  inducing  peristaltic  action. 

Pectin  is  a  polysaccharide  contained  in  the  juices  of  some 
fruits,  e.g.  red  currants,  and  obtained  from  the  pulp  of  many 
fruits  and  vegetables,  and  from  the  inner  peel  of  oranges 
and  lemons  upon  boiling  with  water.  The  addition  of  alcohol 
to  such  juices  or  extracts  precipitates  the  pectin  as  a  jelly. 
If  the  solutions  are  rich  enough  in  pectin,  or  if  they  are  boiled 


THE   CARBOHYDRATES  181 

down  until  they  are  rich  enough  in  pectin,  either  an  acid  or  a 
sugar  will  also  precipitate  the  pectin.  In  the  making  of 
fruit  jellies  and  marmalades  the  acid  naturally  present  in  the 
fruit  juices  and  the  added  sugar  serve  to  precipitate  the 
pectin,  and  the  secret  of  successful  jelly  making  is  to  have 
the  proportions  of  pectin,  water,  acid,  and  sugar  so  adjusted 
that  the  pectin  is  precipitated  as  a  continuous  network, 
filling  the  whole  mold  or  glass  into  which  it  is  poured.  By 
boiling  with  strong  acid,  pectin  can  be  hydrolyzed  to  reduc- 
ing sugars,  but  the  products  obtained  are  probably  not 
identical  with  any  of  the  familiar  sugars  described  above. 

Caramel.  —  When  cane  sugar  is  heated,  it  melts  at  about 
160°  C.  (320°  F.),  and  at  a  little  higher  temperature  begins  to 
decompose.  Effervescence  occurs  due  to  the  evolution  of 
water,  and  the  melted  sugar  acquires  a  dark  color  and  a 
peculiar  flavor.  Sugar  which  has  suffered  this  change  is  said 
to  be  caramelized,  the  color  and  flavor  being  attributed  to 
caramel  (from  the  Latin,  calamellus,  sugar  cane).  In  addition 
to  caramel  the  caramelized  sugar  may  contain  glucose.  When 
caramelized  sugar  is  dissolved  in  water  and  fermented  with 
yeast,  the  glucose  and  unchanged  sucrose  are  destroyed  and 
the  caramel  is  left  unaffected.  Caramel  has  a  dark  brown 
color  and  a  bitter  taste.  It  is  sometimes  used  to  color  milk 
and  cream.  Caramel  is  not  a  single  substance,  but  a  mixture 
of  several  compounds,  all  of  which  differ  from  cane  sugar  in 
that  they  reduce  Fehling's  solution  and  are  not  fermented 
by  yeasts.  Glucose,  melted  and  heated,  also  loses  water  and 
yields  caramel,  and  lactose  yields  a  similar  product  known  as 
lacto- caramel.  The  color  and  flavor  of  taffy  are  due  to  cara- 
mel, and  it  is  produced  in  many  cooking  operations.  Sugar 
which  has  been  melted  and  only  slightly  yellowed  by  heating 
to  1 60°  C.  (320°  F.),  as  in  making  taffy,  is  called  barley 
sugar. 


CHAPTER  XXXIV 
THE  PROTEINS.  I 

THE  most  important  plant  and  animal  substances  contain- 
ing the  element  nitrogen  are  the  proteins.  Being  indispensa- 
ble constituents  of  the  cells  of  which  all  vegetable  and  animal 
organisms  are  made  up,  proteins  are  essential  to  life.  Other 
nitrogen  compounds  than  proteins  exist  in  plants  and  ani- 
mals. Among  such  are  ammonium  salts ;  the  alkaloids,  such 
as  the  caffein  of  tea  and  coffee,  the  nicotine  of  tobacco,  and 
the  quinine  of  Peruvian  bark ;  the  amides,  such  as  asparagine 
and  urea;  the  extractives  of  meat,  such  as  creatine  and 
creatinine. 

These  substances  are  chemically  simpler  than  the  proteins ; 
in  other  words,  they  are  made  up  of  smaller  molecules. 
But  their  relative  abundance  is  so  small  that  when  a  chemist 
wishes  to  estimate  the  quantity  of  protein  in  a  food,  he  com- 
monly ignores  the  presence  of  these  simpler  nitrogenous 
compounds  and  calculates  the  quantity  of  protein  by  mul- 
tiplying the  total  quantity  of  nitrogen  found  by  6.25. 

The  reason  for  using  this  factor  is  that,  on  the  average, 
proteins  contain  16  per  cent  of  nitrogen,  and  16  X  6.25  =  100. 

It  will  be  realized  that  this  is  only  a  rough  way  of  deter- 
mining the  quantity  of  protein  in  a  food,  but  it  is  the  method 
almost  universally  used. 

The  proteins  resemble  the  polysaccharides  in  having  very 
complex  molecules,  in  forming  colloidal  solutions,  and  in 
being  hydrolyzable  into  crystalloid  substances.  The  crystal- 
loid substances  into  which  the  proteins  are  ultimately  con- 
verted by  hydrolysis  are  the  so-called  amino  acids. 

182 


EMIL  FISCHER.  — 1852-. 

A  distinguished  German  chemist,  whose  researches  upon  the  chemistry  of 
the  carbohydrates  and  proteins  have  contributed  much  to  our  knowledge  of 
both  these  classes  of  compounds. 


THE  PROTEINS  183 

An  amine  is  a  compound  constituted  like  ammonia  but  having 
in  place  of  one  (or  more)  of  the  hydrogen  atoms  of  the  ammonia 
molecule  an  organic  radicle  attached  to  the  nitrogen  atom.  Thus  : 

/H  /H  /H  /H 

N^-H  N^-H  N^-H  N^-H 

\H  \CH3  \C2H5  \C6H5 

Ammonia    Methylamine    Ethylamine    Phenylamine 

(Aniline) 

An  ammo  acid  is  a  compound  which  is  at  the  same  time  an 
amine  and  an  acid.  Its  molecule,  therefore,  contains  both  the 
amino,  —  NH2,  and  the  carboxyl,  —  COOH,  groups.  The  simplest 
substances  of  the  class  are  glycine  and  alanine,  which  have  the 
structural  formulas  : 

CH3 

CH2NH2  | 

|  CHNH2 

COOH  | 

COOH 
Glycine  Alanine 

Two  or  more  amino-acid  molecules  can  be  converted  into  a 
peptide  and  water  thus  : 

2  NH2  .  CH2  .  COOH  =  NH2  .  CH2  .  CO  .  NH  .  CH2  .  COOH  +  H2O 

Glycine  Glycyl  glycine,  a  dipeptide 


H2  .  CH2  .  COOH  +  CH3  .  CH  NH2 

CH3  .  CH  NH2  .  CO  .  NH  .  CH2  .  COOH 

Alanyl  glycine,  a  dipeptide 

2  NH2  .  CH2  .  COOH  +  CH3  .  CH  NH2  .  COOH  = 

CH3  .  CH  NH2.  CO  .  NH  .  CH2  .  CO  .  NH  .  CH2  .  COOH  +  2  H2O. 

Alanyl  glycyl  glycine,  a  tripeptide 

Upon  hydrolysis  these  reactions  are  reversed,  the  peptides  being 
resolved  into  amino  acids.  Now,  it  is  probable  that  the  proteins 
of  plants  and  animals  are  peptides  made  up  of  a  great  many  amino- 
acid  molecules,  joined  together  in  the  way  indicated  above. 
Peptides  made  up  of  a  large  number  of  amino-acid  molecules  are 
designated  polypeptides.  The  proteins,  therefore,  are  regarded  as 
polypeptides. 


1 84  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

In  all,  about  twenty  amino  acids  have  been  obtained  from  the 
various  proteins  by  hydrolysis,  and  a  single  protein  may  yield 
all  of  them,  and  usually  does  yield  the  greater  number  of  them. 
Some  of  these  twenty-odd  amino  acids  contain  more  than 
one  amino  group,  some  more  than  one  carboxyl  group,  some 
contain  sulphur,  and  there  are  various  other  complications. 

The  proportions  of  the  various  amino  acids  yielded  by  the 
various  proteins  differ  widely.  For  instance,  comparing  the 
following  proteins  —  casein  from  milk,  gelatin  prepared  from 
the  tendons  of  beef,  gliadin  from  wheat,  and  zein  from  corn  — 
we  find  that  no  glycine  is  yielded  by  casein,  gliadin,  or  zein, 
while  the  amount  yielded  by  gelatin  amounts  to  one  sixth  of 
the  weight  of  the  gelatin.  Again,  while  gelatin  yields  only  0.6 
per  cent  of  alanine,  casein  yields  1.5,  gliadin  2,  and  zein  nearly 
10  per  cent  of  this  amino  acid.  Once  more,  tryptophane,  one 
of  the  very  complex  amino  acids,  is  not  found  among  the 
hydrolysis  products  of  gelatin  or  of  zein,  but  gliadin  yields 
i  per  cent  and  'casein  i \  per  cent  of  this  substance. 

In  addition  to  amino  acids,  ammonia  is  formed  in  the 
hydrolysis  of  proteins,  and  from  certain  classes  of  proteins— 
the  so-called  "  conjugated  "  proteins  —  still  other  products 
are  obtained.  Thus,  hemoglobin,  the  red  coloring  matter  of 
the  blood,  yields  a  pigment  containing  iron;  casein  (the 
curd  of  milk)  and  wtellin  of  egg  yolk  yield  phosphorus  com- 
pounds ;  the  mucins  yield  carbohydrates ;  and  nudeins  yield 
nucleic  acid,  a  complex  organic  acid  containing  phosphorus. 
The  amino  acids  and  the  other  groups  which  enter  into  the 
molecules  of  the  more  complex  proteins  are  often  referred  to 
figuratively  as  the  "  building  stones  "  of  the  protein  mole- 
cules. "  Native  "  proteins  (i.e.  such  as  exist  in  plant  and 
animal  tissues  and  fluids)  may  be  divided  into  two  classes :?. 

1.  Simple  proteins,  which  yield  no  hydrolysis  products 
other  than  amino  acids  and  ammonia. 

2.  Conjugated   proteins,    which    yield    other    hydrolysis 
products  in  addition  to  amino  acids  and  ammonia. 


THE  PROTEINS  185 

Just  as  in  the  hydrolysis  of  starch,  intermediate  products 
—  soluble  starch,  dextrins,  maltose  —  between  the  starch 
and  its  ultimate  product,  glucose,  were  obtained,  so  also  in 
the  hydrolytic  cleavage  of  proteins,  intermediate  products 
are  obtained.  Some  of  these  products  have  still  the  essential 
characteristics  of  proteins.  When  egg-white  is  heated  above 
73°  C.  (160°  F.),  for  example,  it  hardens  or  "  coagulates." 
It  is  thus  converted  from  a  substance  soluble  in  water  into 
one  which  is  insoluble  but  is  still  essentially  a  protein.  It  is 
believed  that  this  change  is  due  to  slight  hydrolysis  or  hydra- 
tion  of  the  protein  molecule.  Similarly,  the  soluble  caseinogen 
of  milk  is  readily  converted  into  the  insoluble  protein,  casein, 
by  the  action  of  the  ferment  rennin ;  and  the  soluble  fibrino- 
gen  of  the  blood  clots  into  fibrin  when  the  blood  is  exposed 
to  air.  Such  slightly  altered  proteins  are  called  "  derived 
proteins  "  or  protein  derivatives.  Another  class  of  derived 
proteins  are  obtained  by  further  hydrolysis  of  such  primary 
derivatives  as  coagulated  egg  albumin,  fibrin,  and  casein. 
Such  hydrolysis  can  be  accomplished  by  the  action  of  diges- 
tive ferments  (such  as  the  pepsin  found  in  the  stomach  and 
the  trypsin  found  in  the  small  intestines)  and  the  products 
are  substances  soluble  in  water  and  not  coagulated  by  heat. 
The  substances  so  produced  are  called  proteases  and  peptones. 
Proteoses  are  more  complex  and  less  soluble  in  salt  solutions 
than  peptones,  but  no  very  sharp  line  of  distinction  can  be 
drawn  between  the  two  classes  of  compounds.  The  term 
peptone  was  formerly  applied  to  both,  and  commercial 
"  peptone  "  consists  largely  of  proteoses. 

Protein  Tests 

The  following  are  some  of  the  most  general  tests  for 
proteins; 

i.   Decomposition  Test.  —  Proteins  when  subjected  to  dry 
heat  (e.g.  in  a  test  tube)  give  off  vapors  having  an  alkaline 


186  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

reaction  and  a  characteristic,  disagreeable,  "  empyreumatic  " 
odor  —  that  of  burning  meat,  feathers,  leather,  hair,  wool,  etc. 
When  the  protein  is  mixed  with  lime  and  heated,  the  odor 
of  ammonia  is  distinctly  noticeable. 

Experiment  104. 

Materials : 

Egg  albumin,  dry. 

Blood  albumin,  dry. 

Gelatin. 

Casein. 

Quicklime. 

Turmeric  paper. 

Red  litmus  paper. 

Heat  a  little  of  each  of  the  proteins  in  a  dry  test  tube.  Note 
the  odor.  Add  quicklime  and  heat  again.  Note  odor  and  hold 
turmeric  paper  and  red  litmus  paper  at  the  mouth  of  the  test  tube. 
Also  expose  turmeric  paper  and  red  litmus  paper  to  ammonia  gas 
by  holding  them  to  the  open  mouth  of  the  ammonium  hydroxide 
reagent  bottle. 

2.  Xanthoproteic  Test  (Greek,  xanthos  =  yellow).  —  Pro- 
teins heated  with  concentrated  nitric  acid  impart  a  yellow 
color  to  the  acid,  owing  to  the  formation  of  xanthoproteic 
acid.  If  the  acid  be  then  neutralized  with  ammonia,  the 
color  deepens.  ^ 

Experiment  105. 

Materials : 

The  same  proteins  as  for  Experiment  104. 
Sugar. 

Gently  heat  a  little  of  each  of  the  proteins  with  concentrated 
nitric  acid.  Note  the  coloration.  Cool  the  tube,  and  then  neu- 
tralize the  acid  with  ammonium  hydroxide.  Heat  a  very  little 
sugar  with  nitric  acid  in  the  same  manner  as  the  proteins.  Is  the 
acid  colored  by  the  sugar?  Cool  and  neutralize  with  ammonia. 
In  making  the  xanthoproteic  tests  on  the  proteins  notice  the  dif- 
ference in  behavior  between  gelatin  and  the  other  proteins. 
Chemically  pure  gelatin  gives  no  xanthoproteic  test.  This  test 
is  due  to  the  action  of  nitric  acid  upon  the  amino  acids  of  a  certain 


THE  PROTEINS  187 

class,  none  of  which  is  yielded  by  the  hydrolysis  of  pure  gelatin. 
Commercial  gelatin,  however,  contains  small  quantities  of  other 
proteins. 

3.  Millon's  Test.     Proteins  boiled  with  Millon's  reagent 
(prepared  by  dissolving  mercury  in  its  own  weight  of  con- 
centrated nitric  acid,  diluting  with  twice  the  volume  of  water, 
and  allowing  to  settle)  yield  a  red  precipitate  which  collects 
at  the  surface  of  the  liquid. 

Experiment  106. 

Materials : 

The  same  proteins  as  for  Experiment  104. 

Boil  small  portions  of  the  proteins  in  test  tubes  with  Millon's 
reagent.  Note  the  difference  in  behavior  between  gelatin  and 
the  others.  Pure  gelatin  gives  no  Millon's  test,  this  reaction 
being  due  to  an  amino  acid  of  the  same  class  as  those  to  which 
the  xanthoproteic  test  is  due. 

4.  Biuret  Test.  —  Proteins  dissolved  in  strong  alkali  and 
treated  with  minute  quantities  of  copper  sulphate  give  a 
violet  to  blue  coloration.     The  test  takes  its  name  from  the 
substance    with    which    it    was    first    obtained.     Biuret, 
NH2 .  CO  .  NH  .  CO  .  NH2,   although  neither  a  protein,   a 
peptide,  nor  an  amino  acid,  gives  a  coloration  like  that  given 
by  the  proteins. 

Experiment  107. 

Materials : 

The  proteins  used  in  Experiment  104. 
Peptone. 

Dissolve  a  little  of  each  in  a  50  per  cent  solution  of  potassium 
hydroxide.  To  a  test-tubeful  of  water  add  a  drop  or  two  of  copper 
sulphate  solution.  Add  a  few  drops  of  this  diluted  copper  sul- 
phate solution  to  the  alkaline  solutions  of  the  proteins.  Note 
any  differences  observed. 


CHAPTER  XXXV 

THE   PROTEINS.   II 

WE  have  seen  that  the  "  building  stones "  which  go  to 
make  up  the  molecules  of  proteins  are  numerous  and  varied.- 
We  have  also  seen  that  a  single  pair  of  these  amino  acids  can 
be  joined  together  into  two  different  products,  e.g.  glycine 
and  alanine  into  either  glycyl  alanine  or  alanyl  glycine. 
Remembering,  now,  that  the  protein  molecules  are  built  up, 
not  of  two,  but  of  a  large  number  of  building  stones,  we  can 
realize  that  a  great  many  different  kinds  of  protein  molecules 
might  be  constructed,  not  only  by  varying  the  selection  of 
the  building  stones,  but  also  by  varying  their  arrangement. 

Whether  this  be  the  explanation  or  not,  it  is  certainly  true 
that  the  proteins  exhibit  a  remarkable  diversity  of  physical 
properties,  particularly  as  regards  their  solubilities.  It  is 
customary  to  attempt  to  classify  the  proteins  according  to 
their  solubilities  in  a  number  of  solvents. 

The  albumins  dissolve  in  water  and  are  coagulated  by 
heat.  Egg  albumin  (ovalbumin),  milk  albumin  (lactalbumin), 
and  blood  albumin  (seralbumin)  are  typical  examples. 

The  term  albumins  has  been  much  used  as  the  general  class 
name  for  proteins'.  The  definition  here  given  is  that  now  rec- 
ognized by  the  leading  American  and  British  societies  of  physi- 
ology and  biological  chemistry.  Other  terms  formerly  used  as 
synonyms  for  the  modern  term  proteins  are  proteids  and 
albuminoids.  The  societies  referred  to  have  agreed  to  drop  the 
word  proteid  altogether.  The  English  societies  also  drop  albu- 
minoid, while  the  American  societies  use  it  to  designate  a 
special  class  of  proteins.  (See  below.) 

188 


THE   PROTEINS  189 

Experiment  108.  —  Coagulation  of  Egg  Albumin. 

Materials : 

Fresh  white  of  egg. 
Thermometer. 

Fill  a  test  tube  to  the  depth  of  i^  to  2  inches  with  fresh  white  of 
egg.  Put  a  thermometer  into  the  liquid  and  place  the  tube  in 
a  beaker  of  cold  water  over  a  low  flame.  Note  the  temperature 
at  which  the  albumin  coagulates  (whitens).  Express  this  tem- 
perature in  Fahrenheit  and  in  Centigrade  degrees. 

It  is  because  of  the  coagulating  effect  of  heat  on  albumins 
and  on  some  other  classes  of  proteins  that  in  washing  dishes 
which  have  held  uncooked  foods,  such  as  milk  or  eggs,  it  is 
better  to  rinse  with  cold  water  before  applying  hot  water. 

The  globulins  are  insoluble  in  water  but  soluble  in  dilute 
solutions  of  the  neutral  salts  of  strong  acids  with  strong 
bases.  They  are,  however,  insoluble  in  concentrated  solu- 
tions of  these  same  salts.  (The  albumins  are  soluble  both  in 
dilute  and  in  saturated  sodium  choride  and  magnesium 
sulphate.) 

Among  the  globulins  are  the  myosin  of  meat,  the  fibrinogen 
of  blood  (the  change  of  which  into  fibrin  is  the  cause  of  blood 
clotting),  serum  globulin,  which  remains  in  solution  in  the 
serum  of  blood,  and  ovoglobulin,  a  constituent  of  egg-white. 
Edestin  is  a  globulin  found  in  many  plant  seeds,  including  the 
cereals,  flaxseed,  and  hempseed.  Legumin  is  a  globulin  found 
in  peas  and  beans. 

Experiment  109. 

Materials : 

Hempseed,  crushed. 
5  per  cent  solution  of  common  salt. 

Cover  a  handful  of  crushed  hempseed  with  5  per  cent  sodium 
chloride  and  heat  to  60°  C.  for  about  half  an  hour.  Moisten 
a  filter  with  hot  5  per  cent  sodium  chloride  solution  and  filter  the 
hot  liquid  through  it.  Allow  the  filtrate  to  cool.  Part  of  the 
edestin  crystallizes  out  on  cooling.  Filter  off  a  little  of  this 
crystallized  edestin  and  wash  it  in  test  tubes  with  water.  Boil  a 


ELEMENTARY  HOUSEHOLD   CHEMISTRY 

little  of  it  with  Millon's  reagent.  Does  it  behave  like  a  protein? 
Treat  three  equal  portions  of  the  edestin  with,  respectively,  (a) 
distilled  water,  (b)  a  5  per  cent  sodium  chloride  solution,  (c)  a 
saturated  sodium  chloride  solution,  warming  each  to  about  60°  C. 
Which  of  these  three  liquids  is  the  best  solvent  for  edestin  ? 

The  most  important  proteins  of  the  interior  of  the  wheat 
grain  (and  therefore  of  white  flour)  are  those  which  are  con- 
tained in  the  gluten.  Gluten,  which  —  as  is  evident  from 
the  method  of  its  preparation  from  flour  —  is  insoluble  in 
water,  contains  as  its  chief  constituents  two  proteins  called 
glutenin  and  gliadin.  Both  of  these  constituents  are  insoluble 
in  water.  Glutenin,  however,  is  soluble  in  very  dilute  acids 
and  alkalies  and  is  representative  of  a  class  of  proteins  known 
as  glutelins,  which  behave  similarly.  Gliadin  is  soluble  in  a 
mixture  of  alcohol  and  water  containing  60  to  70  per  cent  of 
the  former.  It  is,  however,  insoluble  in  absolute  alcohol. 

Experiment  no.  —  Preparation  of  Wheat  Gluten  from  Flour. 

Materials : 

Wheat  flour,  strong  and  not  over  nine  months  old. 
Cheesecloth. 

Mix  30  grams  flour  with  5  cc.  water  to  form  a  stiff  dough. 
Knead  in  the  hand  in  a  stream  of  running  water  until  the  water 
runs  through  clear.  (What  constituent  of  the  flour  is  carried 
out  by  the  water,  rendering  it  turbid?)  Examine  the  residue  of 
gluten  left  in  the  hand.  Note  its  color  and  elasticity.  The 
quality  of  flour  depends  not  only  on  the  quantity,  but  also  on  the 
quality  of  the  gluten  contained  in  it.  The  gluten  of  good  flour  is 
yellow,  tough,  and  elastic.  That  of  aged  flour  is  grayish  and 
"  short  "  or  friable. 

Experiment  in.  —  Gliadin. 

Materials : 

Gluten  from  Experiment  no. 
Mortar  and  pestle. 

Put  the  gluten  from  Experiment  no  in  a  mortar,  cover  it  with 
a  mixture  of  5  cc.  water  and  15  cc.  alcohol  and  rub  well  with  the 
pestle.  Filter.  To  one  portion  of  the  filtrate  add  water,  to  an- 
other alcohol.  What  effect  does  each  have  ?  Explain. 


THE   PROTEINS  191 

The  albuminoids  or  scleroproteins  (from  the  Greek, 
skleros,  hard)  are  a  class  of  simple  proteins  characterized  by 
great  insolubility.  They  include  collagen,  the  protein  of  car- 
tilage, skin,  and  bone ;  and  keratin,  the  protein  of  hair,  horns, 
hoofs,  nails,  etc.  Collagen  is  converted  by  hydrolysis  into 
gelatin  which  is  soluble  in  hot  water,  forming  a  solution  which 
sets  to  a  jelly  on  cooling.  Commercial  gelatin  is  usually 
made  from  bones  by  treatment  with  hydrochloric  acid,  fol- 
lowed by  treatment  with  boiling  water  or  steam.  Glue  is  a 
crude  form  of  gelatin  made  fromiVhoofs  and  hide  clippings. 
Isinglass  is  a  natural  gelatin  founoin  the  swimming  bladders 
of  certain  fishes. 

The  keratins  contain  a  high  proportion  of  sulphur.  Hair 
and  wool  are  therefore  characterized  by  decided  tests  for 
sulphur  —  a  fact  which  is  used  to  distinguish  these  fibers 
from  silk,  which  is  also  essentially  protein  but  contains  no 
sulphur.  (See  Chapter  XL.) 

Experiment  112. 

Materials : 
Sulphur. 
Wool,  undyed. 

Egg  albumin,  raw,  coagulated  (hard  boiled),  or  dried. 
Egg  yolk,  raw  or  coagulated. 
Silk. 

(a)  Prepare   sodium   plumbite   solution   by   adding   sufficient 
sodium  hydroxide  solution  (5  to  10  cc.)  to  i  cc.  lead  acetate  solu- 
tion to  redissolve  (on  warming)  the  precipitate  which  forms  at  first. 

(b)  Boil  a  little  sulphur  with  sodium  hydroxide  solution.     Add 
a  little  of  the  sodium  plumbite.     The  black  precipitate  which 
forms  is  lead  sulphide,  PbS. 

(c)  Boil  a  small  quantity  of  the  wool  with  sodium  hydroxide. 
Add  to  sodium  plumbite  solution  and  boil.     Add  sufficient  water 
to  enable  you  to  see  through  the  liquid.     Has  a  black  precipitate 
(lead  sulphide)  formed  ? 

(d)  Repeat  (c)  using  egg  albumin  instead  of  wool. 

(e)  Repeat  (c)  using  yolk  of  egg. 
(/)  Repeat  (c)  using  silk. 


CHAPTER  XXXVT 
THE  FUNCTIONS  OF  FOOD 

THE  functions  of  food  are : 

1.  To  supply  building  material  for  the  growth  and  repair 
of  body  tissue. 

2.  To  furnish  energy  for  the  internal  and  external  work  of 
the  body  and  heat  to  keep  the  body  warm. 

3.  To  regulate  the  physiological  processes,  i.e.  the  chemical 
and  physical  changes  occurring  in  the  body. 

I.   Food  as  Building  Material 

The  human  body  is  composed  of  the  same  classes  of  sub- 
stances as  foods.  It  is  made  up  approximately  as  follows : 

APPROXIMATE  COMPOSITION   OF  HUMAN  BODY 

PER  CENT 

Water,  about       65 

Proteins,  about    ........       18 

Fat,  about       12   (varying  greatly) 

Carbohydrates,  less  than i 

Ash,  about 4  to  5. 

The  amount  of  carbohydrates  in  the  body  is  not  only 
very  small,  but  also  exceedingly  variable.  The  amount  of 
fat  is  also  widely  variable  and  may  fall  very  low  without 
interfering  with  the  normal  physiological  processes. 

Proteins  are  essential  constituents  of  all  living  cells,  both 
vegetable  and  animal.  There  can  be  no  life  without  them. 
Plants  manufacture  their  own  proteins  from  inorganic  ma- 
terials, making  use  of  the  carbon  dioxide  which  they  obtain 
from  the  air  and  of  the  water  and  nitrogen  compounds  which 

192 


WILBUR  OLIN  ATWATER.  — 1844-1907. 

Distinguished  for  his  researches  on  the  chemistry  of  nutrition.  Professor 
of  Chemistry  in  Wesleyan  University,  Middletown,  Connecticut,  from  1873, 
the  first  director  of  an  American  agricultural  experiment  station,  and  the  first 
Director  of  the  Office  of  Experiment  Stations  of  the  United  States  Depart- 
ment of  Agriculture,  Atwater  devoted  special  attention  to  agricultural  chem- 
istry and  to  problems  of  human  nutrition.  Under  bis  direction  numerous 
analyses  and  determinations  of  digestibility  of  American  food  materials  were 
made.  The  respiration  calorimeter  described  in  the  text  was  devised  for  the 
purposes  of  these  nutrition  investigations. 


THE  FUNCTIONS  OF  FOOD  193 

they  obtain  from  the  soil  to  build  up  the  large  and  complex 
protein  molecules. 

Animals  have  not  this  power  of  building  up  proteins  from 
inorganic  materials.  It  appears  doubtful  whether  they  can 
synthesize  them  even  from  simpler  organic  substances  not 
derived  from  other  proteins.  For  the  most  part,  at  any  rate, 
they  merely  take  proteins  ready-made  and  convert  them 
into  other  proteins. 

Since  animals  must  have  proteins  to  form  and  repair  their 
body  tissues,  and  since  they  cannot  make  proteins  except 
from  other  proteins,  it  follows  that  proteins  are  absolutely 
essential  constituents  of  the  food  of  all  animals.  However 
generous  the  supply  of  carbohydrates  and  fats,  the  animal 
cannot  thrive  nor  even  continue  to  live  without  a  constantly 
renewed  supply  of  protein.  The  term  "  protein  "  (from  a 
Greek  verb  signifying  to  take  the  first  place)  is  applied  to  this 
class  of  compounds  on  account  of  its  unique  and  preeminent 
importance  in  relation  to  life. 

Some  of  the  ash  constituents  of  food  are  also  of  special 
importance  as  building  material.  Bones  contain  a  large 
proportion  of  calcium  phosphate.  This  salt  constitutes  more 
than  half  the  weight  of  the  dry,  or  more  than  one-fourth  the 
weight  of  the  fresh,  bone.  Calcium  salts  and  phosphorus 
compounds  are  therefore  of  great  importance  in  foods  in 
relation  to  the  growth  and  maintenance  of  the  skeletal  frame- 
work of  the  body.  Iron  is  an  essential  constituent  of  hemo- 
globin, the  protein  of  the  red  corpuscles  of  the  blood.  Hence, 
an  abundant  supply  of  iron  in  the  food  is  important  for  the 
maintenance  of  health,  and  still  more  so  when  the  blood  re- 
quires enrichment ;  e.g.  in  cases  of  anaemia. 


II.  Food  as  Fuel 

The  chief  ultimate  products  of  the  chemical  changes  which 
occur  in  the  body  are  the  carbon  dioxide  given  off  from  the 


194  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

lungs ;  the  water  excreted  by  the  lungs,  skin,  and  kidneys ; 
and  the  urea  and  salts  excreted  by  the  kidneys.  Urea  is  a 
nitrogenous  organic  compound  of  the  formula,  CO^Hj,  and 
is  plainly  derived  from  the  proteins.  As  far  as  the  organic 
foodstuffs  are  concerned,  then,  we  may  summarize  the  chemi- 
cal reactions  of  the  body  as  follows : 

Fats  and  carbohydrates  oxidize  to  carbon  dioxide  and  water. 

Proteins  oxidize  to  carbon  dioxide,  water,  and  urea. 

The  foregoing  paragraph  must  be  understood,  not  as  an  adequate 
account  of  the  chemistry  of  nutrition,  but  only  as  the  roughest 
outline  of  the  sum  of  the  numerous  changes  involved.  The  re- 
actions by  which  the  different  classes  of  foods  are  digested,  ab- 
sorbed, stored,  and  utilized  as  fuel  are  very  complicated.  Some 
reference  to  these  processes  —  especially  to  digestion  and  absorp- 
tion —  will  be  made  later. 

Again,  the  products  enumerated  above  are  by  no  means  all  the 
compounds  excreted  from  the  body.  In  addition  to  water,  salts, 
and  urea,  the  urine  contains  notable  quantities  of  three  other 
nitrogenous  compounds  of  importance,  namely,  uric  acid, 
creatinine,  and  hippuric  acid,  and  also  notable  quantities  of  a 
number  of  sulphur  compounds.  The  bowel  excrement  (feces), 
although  consisting  in  part  of  undigested  food  —  more  or  less 
fermented  and  putrefied  by  bacteria  -«-  also  contains  a  certain 
proportion  of  substances  derived  from  the  digested  and  absorbed 
food.  Among  these  are  compounds  of  iron,  phosphorus,  rriagnesium, 
and  calcium. 

These  ultimate  products  of  the  chemical  changes  occurring 
in  the  body  are  produced  by  the  combining  of  the  oxygen  of 
the  air  with  the  elements  of  the  digested  and  assimilated 
food.  And  it  is  to  be  noted  that  the  products  of  oxidation  of 
the  fats  and  carbohydrates  in  the  body  are  exactly  the  same 
as  those  which  are  produced  by  the  rapid  oxidation,  i.e.  com- 
bustion, of  these  substances. 

When  food  is  oxidized  in  the  body,  then,  the  chief  chemical 
products  are  the  same  as  those  which  would  be  obtained  if 
the  food  were  burned  in  a  stove  or  in  a  calorimeter.  (See 
p.  52.)  For  fats  and  carbohydrates  this  statement  is  literally 


FIG.  39.  —  The  A  twater-Rosa  Respiration  Calorimeter.     Interior  View. 

From  Bulletin  175,  Office  of  Experiment  Stations,  U.  S.  Department  of  Agriculture, 
by  permission. 


THE  FUNCTIONS   OF  FOOD  1 95 

true.  In  the  case  of  proteins  it  requires  the  modification 
that  the  nitrogen,  which  in  combustion  is  given  off  as  the 
free  element,  is  excreted  from  the  body  combined  with  a 
certain  amount  of  carbon,  hydrogen,  and  oxygen,  chiefly  as 
urea,  CON2H4,  a  compound  which  can  itself  be  further  oxi- 
dized (e.g.  by  combustion)  to  carbon  dioxide,  water,  and  free 
nitrogen. 

When  burned  in  a  furnace,  fats  and  other  organic  food 
constituents  produce  heat,  a  part  of  which  may  be  converted 
into  work  by  such  a  device  as  a  steam  engine.  A  fat  oxidized 
in  the  body  also  produces  work  and  heat,  the  work-producing 
mechanism  being  the  muscles. 

We  can  easily  measure  the  quantity  of  heat  which  any 
pure  foodstuff  or  any  mixed  food  is  capable  of  producing 
when  rapidly  oxidized.  This  measurement  can  be  made  in 
•  exactly  the  same  way  as  in  the  case  of  fuels,  i.e.  by  burning 
a  small  weighed  sample  of  the  food  or  foodstuff  in  com- 
pressed oxygen  in  the  bomb  calorimeter  (see  Fig.  32,  p.  55), 
and  noting  the  quantity  of  heat  set  free.  It  is  also  possible 
to  measure  the  quantity  of  heat  set  free  by  a  man  or  an 
animal  maintained  on  a  certain  diet.  This  is  done  by  con- 
fining the  man  or  animal  to  the  chamber  of  an  animal  calo- 
rimeter —  an  apparatus  which  measures  the  quantity  of  heat 
given  off  from  his  body. 

Figure  39  is  an  interior  view  of  a  "  respiration  "  calorimeter 
designed  by  the  late  Professor  W.  O.  Atwater  of  Wesleyan  Uni- 
versity, Middletown,  Conn.,  and  Professor  E.  B.  Rosa  of  the  same 
institution,  for  experiments  upon  man.  This  apparatus  was  so 
constructed  that  no  heat  could  escape  through  the  walls  of  the 
chamber.  The  heat  given  off  by  the  occupant  was  absorbed  by 
a  current  of  water  flowing  through  the  pipes  at  the  top  of  the 
chamber.1  The  quantity  of  water  flowing  through  these  pipes 
was  measured  and  also  its  temperature  as  it  entered,  and  again 

1  In  the  illustration  these  pipes  are  partly,  but  not  entirely,  concealed  by 
metal  "shields,"  which  could  be  raised  or  lowered  to  regulate  the  rate  at  which 
the  heat  was  taken  up  by  the  water. 


196  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

as  it  left,  the  chamber.  The  product  of  the  quantity  of  water 
flowing  in  a  given  time  and  its  rise  of  temperature  represented  the 
number  of  Calories  given  off  by  the  occupant  of  the  chamber. 
The  chamber  had  a  tightly  sealed  window  and  a  porthole  or  large 
pipe  through  which  food  and  other  materials  could  be  passed  in 
and  out,  the  porthole  being  kept  closed  at  one  end  whenever  it 
was  opened  at  the  other.  Provision  was  also  made  for  continually 
renewing  the  supply  of  oxygen,  and  the  apparatus  owes  its  name 
of  "  respiration  "  calorimeter  to  the  fact  that  it  was  so  designed 
that  not  only  the  heat,  but  also  the  amounts  of  carbon  dioxide 
and  water  produced,  and  (as  later  developed)  the  quantity  of 
oxygen  used  by  the  subject  of  the  experiment  could  be  measured. 
Experiments  with  this  apparatus  were  sometimes  continued  for 
periods  of  ten  or  twelve  days. 

This  apparatus  was  greatly  improved  and  eventually  rebuilt 
by  Dr.  F.  G.  Benedict.  Figure  40  gives  a  view  of  one  form  of 
apparatus  now  in  use,  showing  the  exterior  of  the  respiration 
chamber  and  the  apparatus  used  in  measuring  the  heat  given  off 
and  the  carbon  dioxide  and  water  excreted  by  the  occupant  of  the 
chamber.  An  observer  is  shown  seated  at  the  observer's  table, 
a  post  which  is  manned  night  and  day  during  the  course  of  an 
experiment.  This  observer  is  making  the  temperature  observa- 
tions and  so  controlling  the  instrument  that  no  heat  can  pass 
through  the  walls  of  the  respiration  chamber.  In  front  of  the 
observer  is  a  hanging  support  for  the  galvanometer,  an  electrical 
instrument  used  in  the  temperature  measurements.  On  the  floor 
in  front  of  the  observer  (at  the  right  of  the  picture)  is  a  rack  or 
table  holding  the  apparatus  through  which  the  circulating  air  is 
passed  for  purification  and  analysis  before  being  returned  to  the 
respiration  chamber.  Behind  the  observer's  platform  (i.e.  to  the 
reader's  left)  near  the  floor  is  a  large  cylindrical  vessel  in  which 
the  water,  which  passes  through  the  pipes  in  the  chamber  to  absorb 
the  heat,  is  collected  and  weighed.  And  on  the  extreme  left  of 
the  picture  a  second  experimenter  is  seen  talking  through  a  tele- 
phone to  the  man  inside  the  chamber  who  is  serving  as  the  subject 
of  the  experiment. 

When  such  measurements  are  made,  it  is  found  that  the 
quantity  of  heat  produced  by  the  oxidation  of  a  fat  is  exactly 
the  same  when  this  oxidation  takes  place  slowly  in  the  human 
body  as  when  it  takes  place  instantaneously  in  the  bomb 


THE   FUNCTIONS   OF   FOOD  197 

calorimeter.  The  same  is  true  of  a  carbohydrate  such  as 
starch  or  sugar.  The  quantity  of  heat  produced  by  the 
oxidation  of  a  protein  in  the  body  is  less  than  that  produced 
by  the  combustion  of  the  protein  in  the  bomb ;  but  the  dif- 
ference is  just  the  quantity  of  heat  yielded  by  the  combus- 
tion of  that  quantity  of  urea  and  other  nitrogenous  end 
products  which  would  be  formed  in  the  body  from  the  given 
quantity  of  protein.  In  other  words,  if  we  were  to  allow 
the  oxidation  of  the  protein  to  go  on  in  the  body  of  the  man 
in  the  respiration  calorimeter  and  then  burn  in  the  bomb 
calorimeter  the  excreta  of  the  man,  the  total  heat  obtained 
would  be  the  same  as  if  we  had  burned  the  protein  directly 
in  the  bomb  calorimeter. 

Making  allowance  for  the  average  quantities  of  each 
class  of  foodstuffs  lost  in  digestion  (i.e.  excreted  in  the  feces), 
it  is  found  that  a  pound  of  carbohydrate  in  the  food  yields 
about  1815  Calories,  and  a  pound  of  protein  the  same;  but 
a  pound  of  fat  yields  4080  Calories. 

One  pound  of  fat  is  therefore  equal  in  fuel  value  to  2\  pounds 
of  either  protein  or  carbohydrate. 

Stated  according  to  the  metric  system  of  weights  these 
fuel  values  are : 

Carbohydrates  and  proteins     4  Calories  per  gram 
Fats 9  Calories  per  gram 

When  muscular  work  is  done,  the  heart  beats  more  rapidly 
and  the  breathing  becomes  both  faster  and  deeper.  The 
result  is  a  quickening  of  the  oxidation  processes  in  the  body. 
A  larger  quantity  of  assimilated  food  material  is  oxidized  in 
a  given  time,  and  of  course  a  larger  quantity  of  heat  is  pro- 
duced. But  the  quantity  of  heat  given  off  from  the  body 
does  not  now  amount  to  1815  Calories  for  each  pound  of 
protein  and  each  pound  of  carbohydrate  and  4080  Calories 
for  each  pound  of  fat  oxidized,  for  a  part  of  the  "  fuel  value  " 
of  the  food  is  converted  into  mechanical  work. 


198  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

This  partial  conversion  of  the  fuel  value  or  energy  of  the 
food  into  work  is  accomplished  by  the  muscles  of  the  body 
in  a  way  that  is  not  fully  understood.  In  the  steam  engine 
all  the  energy  of  the  fuel  is  first  converted  into  heat  and  then 
a  part  of  the  heat  is  converted  into  work.  In  the  muscles 
only  a  part  of  the  original  energy  is  converted  into  heat. 
The  remainder  is  apparently  converted  directly  into  work. 
As  much  as  one-fifth  of  the  fuel  value  of  the  foodstuffs  oxidized 
may  be  converted  into  work  by  the  engine  of  the  human 
body,  i.e.  the  muscular  system.  The  work  done  may  be  re- 
converted into  heat,  and  when  this  is  done,  the  total  quantity 
of  heat  produced  —  that  evolved  directly  as  heat  plus  that 
produced  as  work  and  then  converted  into  heat  —  is  equal 
to  1815  Calories  per  pound  of  carbohydrate  and  protein  and 
4080  Calories  per  pound  of  fat  oxidized. 

In  some  of  the  experiments  with  the  respiration  calorimeter 
the  man  in  the  chamber  turned  the  wheel  of  a  stationary 
bicycle  which  was  attached  to  an  electric  dynamo,  the  current 
produced  by  which  was  passed  through  an  incandescent 
electric  light  bulb.  This  device  enabled  the  experimenters 
to  estimate  the  quantity  of  work  done  and  at  the  same  time 
provided  for  the  reconversion  of  the  work  into  heat  within 
the  calorimeter. 

III.   Food  as  a  Regulator  of  Physiological  Processes 

Much  less  is  definitely  known  about  this  function  of  food 
than  about  the  other  two.  It  is  certain,  however,  that  some 
foods  have  a  greater  tendency  to  stimulate  the  activity  of 
the  intestines  than  have  others.  In  other  words  some  foods 
are  laxative,  others  constipating.  Among  the  laxative  foods 
are  fruits,  green  vegetables,  and  the  coarser  cereal  products. 
Fruits  and  green  vegetables  contain  much  water  and  ash 
constituents  or  "  mineral  matter  "  (salts  of  organic  as  well 
as  of  inorganic  acids).  The  outer  portion  of  the  wheat 


THE   FUNCTIONS   OF  FOOD  199 

kernel  (the  bran)  contains  not  only  a  larger  proportion  of 
mineral  matter,  but  also  a  larger  proportion  of  cellulose  —  a 
carbohydrate  which  largely  escapes  digestion.  Cellulose  is 
also  a  prominent  constituent  of  green  vegetables,  such  as 
celery,  lettuce,  radishes,  asparagus,  etc.  The  laxative  effect 
of  coarse  foods  is  commonly  regarded  as  due  to  their  mechan- 
ical stimulation  of  the  intestinal  lining.  But  it  has  been 
shown  in  experiments  upon  cows  that  wheat  bran,  which  in 
its  natural  state  contains  the  potassium,  magnesium,  and  cal- 
cium salts  of  an  organic  acid,  called  phytic  acid,  loses  its 
laxative  effect  when  these  salts  are  removed  from  it.  It  has 
been  found  that  persons  living  exclusively  or  very  largely  on  a 
diet  of  rice  suffer  from  the  disease  beriberi  if  the  bran  of  the 
rice  has  been  polished  off.  While,  therefore,  the  mechanical 
effect  of  coarse  foods  in  stimulating  the  bowels  may  be 
important,  it  seems  probable  that  the  chemical  effects  of 
certain  foods  may  be  equally  or  in  some  cases  even  more 
important. 

Certain  of  the  body  fluids,  such  as  the  gastric  juice,  the 
digestive  fluid  of  the  stomach,  have  an  acid  reaction ;  certain 
others,  such  as  the  saliva,  the  bile,  and  the  blood,  have  an 
alkaline  reaction.  It  is  necessary  to  health  that  the  acidity 
of  the  former  and  the  alkalinity  of  the  latter  should  remain 
within  certain  limits.  The  gastric  juice,  for  example,  must 
not  become  either  neutral  or  too  strongly  acid.  Now  in 
the  oxidation  processes  which  go  on  in  the  body  certain 
constituents  of  food  are  converted  into  acid  products,  cer- 
tain others  into  alkaline  products.  Thus  in  the  oxidation 
of  proteins,  sulphuric  acid  is  produced  from  the  sulphur 
of  the  protein  molecule,  while  the  phosphorus  of  phospho- 
and  nucleo-proteins  and  of  phosphorized  fats,  such  as 
lecithin,  yields  phosphoric  acid.  On  the  other  hand,  the 
salts  of  all  organic  acids  oxidize  to  bicarbonates,  which  may 
acl_aa_alkalies. 

An  excess  of  acid-producing  constituents  in  the  food  is 


200  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

apt  to  lead  to  physiological  disturbances.  The  foods  in 
which  acid-producing  elements  predominate  are  meats,  eggs, 
and  cereals.  In  vegetables,  fruits,  and  milk  the  base-form- 
ing elements  predominate. 

For  a  fuller  discussion  of  the  chemistry  of  nutrition  the  reader  is  referred  to 
Sherman's  "  Chemistry  of  Food  and  Nutrition."    New  York,  191 1. 


CHAPTER  XXXVII 
THE  DIGESTION   OF  FOOD 

IN  order  to  reach  the  tissues  it  is  to  repair  or  the  muscles 
for  whose  activities  it  is  to  serve  as  fuel  material,  the  food 
taken  into  the  alimentary  canal  must  be  absorbed  into  the 
circulating  fluids  of  the  body,  the  blood  and  lymph.  To  get 
into  these  fluids  it  must  pass  through  the  membranous 
envelopes  of  the  vessels  containing  them,  the  capillaries 
(small  blood  vessels)  and  lacteals  (lymph  vessels).  These 
vessels  are  especially  abundant  in  the  folds  and  villi  of  the 
small  intestine,  which  is  the  chief  seat  of  absorption.  Absorp- 
tion, however,  occurs  also  to  a  slight  extent  in  the  stomach 
and  to  a  considerable  extent  in  the  large  (lower)  intestine. 

Now,  chemical  compounds  of  different  classes  show  strik- 
ing differences  in  their  ability  to  pass  through  membranes  of 
a  colloidal  nature,  such  as  make  up  the  linings  of  the  diges- 
tive organs  and  the  envelopes  of  the  capillaries  and  lacteals. 
Such  differences  are  illustrated  in  the  following  experiments, 
although  it  is  only  fair  to  premise  that  some  substances 
which  do  pass  through  the  membranes  used  in  the  experi- 
ments do  not  pass  through  the  living  membranes  of  the 
digestive  organs. 

Experiment  113. 

Materials : 

Parchment  filters  or  parchment  tubing. 
Glass  jars  or  large  beakers. 
Glucose  (dextrose). 
Fructose  (levulose). 
Cane  sugar. 
Maltose. 
Dextrin. 

Starch  paste,  prepared  as  in  Experiment  101  (p.  170). 
201 


202 


ELEMENTARY    HOUSEHOLD    CHEMISTRY 


Put  solutions  of  the  carbohydrates  named  above  (about  one 
part  carbohydrate  to  ten  parts  water)  into  the  parchment  filters 
or  into  pieces  of  the  tubing,  being  careful  to  get  none  of  the  solu- 
tion on  the  outer  surface  of  the  parchment.  Add  a  drop  of  chloro- 
form to  each  to  prevent  the  growth  of  microorganisms. 

Suspend  the  papers  in  jars  or  beakers  of  distilled  water.  If 
tubing  is  used,  both  ends  should  be  suspended  above  the  surface 

of  the  water,  making  a  U-shaped 
tube  dipping  beneath  the  surface 
of  the  water.  (See  Fig.  41.)  Allow 
to  stand  overnight.  Then  care- 
fully withdraw  portions  of  the 
outer  liquids  from  the  bottom  of 
the  jars  with  pipettes  and  test  for 
the  carbohydrates  used,  making 
parallel  tests  with  some  of  the 
liquids  from  the  interior  of  the 
parchment  vessels.  For  tests  see 
your  record  of  Experiments  99  to 
101.  Dextrin  is  tested  for  by  add- 
ing the  liquid  to  a  solution  of  iodine 
FIG.  41.  —  Apparatus  for  the  study  diluted  so  as  to  appear  yellow. 
of  the  diffusibility  of  carbohydrates  Dextrin  changes  the  color  to  red. 
through  parchment  paper.  -r.  i  -11 

Parchment   paper  is   made  by 

dipping  paper  into  strong  sulphuric  acid  and  then  thoroughly 
washing.  This  treatment  greatly  reduces  the  porosity  of  the 
paper  by  converting  some  of  the  cellulose  into  a  more  bulky  sub- 
stance. (See  Experiment  139,  p.  232.) 

Experiment  114. 

Materials : 

Goldbeater's  skin. 

The  same  carbohydrates  as  in  preceding  experiment. 

Select  test  tubes  with  evenly  flanged  tops ;  heat  the  closed  ends 
in  the  flame  and  blow  them  out  while  soft,  thus  forming  a  tube 
open  at  both  ends.  Cut  the  goldbeater's  skin  into  squares  of 
about  i^  inches  and  bind  these  tightly  over  the  flanged  ends  of  the 
tubes  with  thread.  To  make  sure  that  the  tubes  are  tightly  closed 
with  the  skin,  fill  them  with  water.  The  water  will  gradually 
pass  through  the  skins,  but  will  not  flow  in  a  stream  nor  drop  rapidly 
if  the  skin  is  perfect  and  is  properly  bound  to  the  tube. 

Fill   these   tubes   about   three-fourths  with   the  carbohydrate 


THE   DIGESTION   OF   FOOD  203 

solutions  used  in  Experiment  113,  being  careful  to  avoid  wetting 
the  outside  surface.  Place  them  in  beakers  of  distilled  water,  and 
allow  to  stand  overnight.  Pipette  off  portions  of  the  outer  liquids 
from  the  bottom  of  the  beakers  and  test  for  the  carbohydrates  as 
in  the  preceding  experiment. 

Goldbeater's  skin  is  made  from  the  inner  lining  of  the  intestines 
of  cattle. 

The  above  experiments  show  that  colloidally  dissolved 
carbohydrates  will  not  pass  through  the  membranes  used, 
while  the  substances  in  true  solution  (the  crystalloids)  do 
pass  through.  From  the  observations  which  have  been 
made  upon  living  animals,  however,  it  appears  that  even 
some  of  the  crystalloid  substances  cannot  pass  through  the 
envelopes  of  the  blood  and  lymph  vessels.  The  substances 
which  will  not  pass  through  are  those  made  up  of  large  mole- 
cules. Thus  in  some  cases  monosaccharides  pass  through 
but  disaccharides  do  not. 

It  would  appear  from  experiments  upon  animals  that,  as  a 
preliminary  to  absorption  and  utilization,  all  carbohydrates 
must  be  changed  into  monosaccharides.  Similarly,  fats  are  not 
absorbed  until  converted  into  fatty  acids  (or  salts  of  fatty  acids, 
i.e.  soaps)  and  glycerol ;  and  proteins  not  until  converted  into 
amino  acids  and,  perhaps,  relatively  simple  polypeptides. 

It  will  be  noticed  that  the  chemical  changes  which  all 
these  nutrients  undergo  preliminary  to  absorption  are  hydro- 
lytic.  In  other  words,  all  nutrients  incapable  of  direct 
absorption  are  converted  into  absorbable  nutrients  by  re- 
action with  water.  But  this  hydrolysis  of  the  complex 
molecules  of  polysaccharides,  proteins,  and  fats  takes  place 
only  in  contact  with  certain  organic  catalytic  reagents, 
known  as  enzymes  or  "  digestive  ferments." 

These  enzymes  are  contained  in  the  digestive  juices  se- 
creted by  cells  in  the  linings  of  the  digestive  organs  or  by 
glands  which  communicate  with  those  organs.  The  digestive 
juices  are : 


204 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


(1)  The  saliva,  secreted  by  glands  in  or  delivering  their 
secretions  into  the  mouth. 

(2)  The  gastric  juice,  secreted  by  certain  cells  of  the  stomach 
wall,  chiefly  in  the  middle  division  of  the  stomach. 

(3)  The  pancreatic  juice,  secreted  by  the  pancreas  and  de- 
livered into  the  small  intestine  (duodenum). 

(4)  The  bile,  secreted  by  the  liver  and  delivered  into  the 
small  intestine. 

(5)  The  intestinal  juice,  secreted  by  certain  cells  of  the 
intestinal  lining. 

All  of  these  but  the  bile  are  known  to  contain  enzymes 
that  promote  the  hydrolysis  of  organic  nutrients.  Of  such 
enzymes  the  following  are  well  known : 

HYDROLYTIC  ENZYMES  OF  THE  DIGESTIVE  FLUIDS.. 


DIGESTIVE 
SECRETION 

ENZYME 

SEAT  OF  ACTION 

COMPOUNDS 
AFFECTED 

PRODUCTS  (OR 
CHIEF  PRODUCTS) 

Saliva 

Ptyalin 

Mouth       and 

Starch 

Dextrin      and 

cardiac  (an- 

maltose 

terior)     end 

of  stomach 

Gastric  juice 

Pepsin 

Pyloric    (pos- 

Proteins 

Proteoses   and 

terior)     end 

peptones 

of  stomach 

Gastric 

Stomach 

Emulsified 

Fatty       acids 

lipase 

fats,    such 

and    glycerol 

as  cream 

Pancreatic 

Amylopsin 

Intestines 

Starch    and 

Maltose 

juice 

dextrin 

Trypsin 

Intestines 

Proteins 

Proteoses,  pep- 

tones,    poly- 

peptides,  and 

amino  acids 

Steapsin 

Intestines 

Fats   (emul- 

Fatty      acids 

sified      by 

and    glycerol 

bile)    - 

Intestinal 

Sucrase 

Intestines 

Sucrose 

Glucose      and 

juice 

(invertase) 

fructose 

Maltase 

Intestines 

Maltose 

Glucose 

Lactase 

Intestines 

Lactose 

Glucose      and 

galactose 

Erepsin 

Intestines 

Proteoses 

Amino      acids 

and     pep- 

and ammonia 

tones 

THE  DIGESTION    OF    FOOD  205 


EXERCISES 

1.  Classify  these  enzymes  as  (i)  Amylases,  (2)  Disaccharases, 
(3)  Lipases,  (4)  Proteases. 

2.  Write  equations  for  the  hydrolysis  of:    (a)   Sucrose,   (6) 
Tristearin,  (c)  Glycyl  glycine. 

The  following  experiments  will  serve  to  illustrate  the  effects 
of  enzymes : 

Experiment  115. —  Action  of  Ptyalin  on  Starch. 

Materials : 

Starch  solution. 

Prepare  a  starch  solution  as  in  Experiment  101  (p.  171),  dilute 
it  with  two  or  three  times  its  volume  of  water,  cool  to  the  tem- 
perature of  the  hand,  add  a  little  of  your  own  saliva,  mix  well 
and  place  in  a  beaker  of  water  at  the  temperature  of  the  hand 
(about  38°  C.).  After  five  or  ten  minutes  pour  off  a  little  of 
the  liquid  into  a  test  tube  containing  iodine  solution.  If  this  test 
shows  starch  to  be  still  present,  add  more  saliva,  allow  the  test 
tube  to  stand  longer  in  the  beaker,  and  repeat  the  iodine  test  at 
intervals.  When  this  test  shows  all  the  starch  to  have  been  trans- 
formed, pour  off  a  little  of  the  liquid  remaining  in  the  test  tube 
into  Fehling-Benedict  solution  and  boil.  What  kind  of  sub- 
stance has  been  formed  from  the  starch  ?  For  comparison  a  little 
of  the  starch  solution  without  saliva  may  be  similarly  treated  and 
tested. 

Experiment  n 6.  —Action  of  Proteolytic  Ferments  (Proteases)  on 

Fibrin. 

Materials : 
Fibrin.1 

Pepsin  solution. 
Trypsin  solution. 

0.4  per  cent  solution  hydrochloric  acid, 
i  .o  per  cent  solution  sodium  carbonate. 

1  The  fibrin,  pepsin,  and  trypsin  may  be  most  conveniently  bought  in  the 
dried  condition.  The  fibrin  should  be  soaked  in  water  for  an  hour  or  more 
before  beginning  the  experiment.  For  the  pepsin  and  trypsin  solutions  o.i 
gram  of  the  commercial  ferments  are  to  be  dissolved  in  one  liter  of  water.  If 
preferred,  fresh  fibrin  may  be  made  by  whipping  freshly  drawn  ox  blood  with 
twigs  to  promote  clotting  and  then  washing  the  clot  with  cold  water  until  the 


206  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Into  each  of  six  test  tubes  put  a  piece  of  fibrin.  Add  respectively 
(i)  5  cc.  water,  (2)  5  cc.  pepsin  solution,  (3)  5  cc.  0.4  per  cent 
hydrochloric  acid,  (4)  2.5  cc.  pepsin  solution  and  2.5  cc.  0.4  per 
cent  hydrochloric  acid,  (5)  5  cc.  trypsin  solution,  (6)  2.5  cc. 
trypsin  solution  and  2.5  cc.  sodium  carbonate  solution. 

Set  the  test  tubes  (labeled)  in  an  empty  beaker  or  in  a  suitable 
rack  and  place  in  a  water  oven  at  40°  C.  Examine  after  24  hours. 
In  which  of  the  tubes  has  the  fibrin  been  dissolved?  Filter 
and  make  the  biuret  test  on  a  portion  of  the  filtrate.  Boil 
another  portion.  What  do  you  infer  from  the  results?  Does 
the  hydrochloric  acid  alone  affect  the  fibrin  in  any  way?  Is  the 
action  of  the  pepsin  affected  by  the  addition  of  hydrochloric  acid  ? 
Is  that  of  the  trypsin  affected  by  the  sodium  carbonate  ? 

It  is  extremely  difficult  to  separate  an  enzyme  from  the 
substances  accompanying  it,  and  it  is  also  difficult  to  deter- 
mine whether  any  given  preparation  is  to  be  regarded  as 
pure.  The  best  preparations  that  have  been  made,  however, 
resemble  the  proteins  in  composition  and  behavior,  and  it  is 
probable  that  enzymes  are  themselves  proteins.  A  pepsin 
preparation  has  been  made  which  was  capable  of  digesting 
500,000  times  its  weight  of  fibrin ;  also  a  pancreatic  amylase 
(amylopsin)  capable  of  digesting  1,000,000  times  its  weight 
of  starch. 

red  color  is  gone.  Pepsin  solution  may  be  prepared  fresh  by  extracting  the 
finely  cut  mucous  membrane  of  a  pig's  stomach  for  24  hours  either  with  0.4  per 
cent  hydrochloric  acid  at  38-40°  C.  or  with  glycerin  at  room  temperature. 
Fresh  trypsin  solution  can  be  made  by  extracting  the  finely  divided  pancreas  of 
the  pig  or  sheep  for  three  days  with  water  containing  5-10  cc.  of  chloroform  or 
with  glycerin.  The  0.4  per  cent  hydrochloric  acid  may  be  made  from  the 
reagent  (2  N)  dilute  hydrochloric  acid  by  diluting  with  18  times  its  volume  of 
water.  The  sodium  carbonate  solution  may  be  made  directly  by  dissolving  i 
gram  anhydrous  sodium  carbonate  in  100  cc.  water. 


CHAPTER  XXXVIII 
FOODS   OF  VEGETABLE   ORIGIN 


TABLES  giving  the  average  composition  and  fuel  value 
of  American  food  materials  are  given  in  Appendix  A.  Table  I 
(pp.  271-277)  comprises  a  classified  selection  of  foods  of  vege- 
table origin.  The  last  four  columns  of  the  table  give  the  es- 
sential information  about  the  edible  portion  of  each  food. 
The  first  column  gives  the  percentage  of  refuse  in  the  food  as 
purchased.  In  comparing  costs  this  must,  of  course,  be  taken 
into  consideration.  Thus,  the  ico-Calorie  portion  of  the 
edible  part  of  a  banana  (the  first  item  in  the  table)  is  3.6 
ounces.  But  the  average  amount  of  refuse  in  a  banana  as 
purchased  is  35  per  cent.  Thus  with  every  65  ounces  of 
edible  banana  we  purchase  35  ounces  of  banana  peel.  The 
ico-Calorie  portion  of  banana  as  purchased  is  therefore  100 
sixty-fifths  of  3.6  ounces,  which  is  equal  to  5.5  ounces. 

EXERCISES 

1.  Calculate  similarly  the  zoo-Calorie  portion  of  the  follow- 
ing foods  as  purchased:    (a)   Grapes,   (b)  Lemons,   (c)   Squash, 
(d)  Green  peas,  (e)  Butternuts. 

2.  From  the  percentage  composition  of  ten  selected  foods,  as 
given  in  the  second  to  fifth  columns  of  the  table,  calculate  the 
number  of  Calories  per  pound,  the  number  of  ounces  yielding  100 
Calories  and  the  number  of  Calories  out  of  every  100  yielded  by 
proteins,  fats,  and  carbohydrates,  respectively.     For  methods  see 
Appendix  A,  pp.  268-270. 

3.  From  the  percentage  composition  of  the  following  foods 
calculate  as  in  Exercise  2  the  number  of  Calories  per  pound,  the 
weight  of  the  zoo-Calorie  portion  in  ounces,  and  the  distribution 
of  the  100  Calories  among  the  three  classes  of  organic  nutrients ; 
also  in  ounces  the  loo-Calorie  portion  of  the  food  as  purchased : 

207 


208 


ELEMENTARY   HOUSEHOLD    CHEMISTRY 


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FOODS  OF  VEGETABLE  ORIGIN  2Op 

The  most  marked  general  characteristic  of  vegetable 
foods  is  the  large  proportion  of  carbohydrates  contained  in 
them.  If  we  except  olives  and  chocolate,  which  contain 
a  large  proportion  of  fat  (olive  oil  and  cocoa  butter) ;  nuts 
and  oatmeal,  which  are  rich  in  both  fat  and  protein ;  and 
mushrooms,  lettuce,  and  the  legumes,  which  are  rich  in  pro- 
tein, we  may  say  that  all  the  vegetable  foods  have  over  three- 
quarters  of  their  total  fuel  value  in  the  form  of  carbohydrates. 
In  many,  such  as  potatoes  and  all  products  of  the  cereal 
grains,  the  predominating  carbohydrate  is  starch.  In  others, 
such  as  fruits,  sugars  and  pectins  are  predominant.  In  a 
few,  such  as  green  vegetables  and  coarse  roots,  e.g.  turnips 
and  radishes,  cellulose  abounds.  But  carbohydrates  in  some 
form  characterize  them  all. 

Experiment  117. 

Materials : 
Potatoes. 

(a)  Pare  and  grate  one  quarter  of  a  potato.  Add  a  little  water 
and  filter.  Boil  a  portion  of  the  filtrate.  Make  the  biuret 
test  on  another  portion.  What  kind  of  substance  have  you  thus 
detected  in  potato  juice  ? 

(6)  Add  a  portion  of  the  filtrate  to  Fehling-Benedict  solution 
and  boil.  What  kind  of  substance  does  this  test  show  the  potato 
juice  to  contain? 

(c)  Place   the  potato  pulp    in  a  cheesecloth  bag.     Allow  a 
stream  of  water  to  run  through  the  bag  into  a  beaker  and  knead 
the  bag.     Continue  until  the  water  runs  through  clear.    Allow 
the  contents  of  the  beaker  to  settle.    Examine  the  residue  left 
in  the  bag.    It  consists  mainly  of  "  fiber  "  or  "  cellulose." 

(d)  When  the  contents  of  the  beaker  have  settled,  remove  a 
portion  of  the  sediment,  boil  it  with  water,  cool,  and  test  with  iodine. 
What  do  you  infer  that  the  sediment  was  ? 

What  three  kinds  of  carbohydrates  have  you  detected  in  the 
potato  ? 

The  water  in  the  potato  may  be  determined  as  in  Expt.  96 
(p.  163),  and  the  ash  by  burning  the  dried  material  in  the  dish, 
avoiding  heating  above  dull  redness.     For  average  results  consult 
Table  I,  p.  272.     The  ash  averages  i.o  per  cent, 
p 


210  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Experiment  118. 

Materials : 
Carrots. 
Beets. 

Grate  a  carrot.  Test  a  portion  of  the  pulp  for  proteins,  using 
two  appropriate  tests.  Digest  a  portion  of  the  pulp  with  cold 
water ;  filter  and  test  the  nitrate  for  (a)  reducing  sugars,  (6)  sucrose. 
(How  ?)  Boil  a  portion  of  the  pulp  with  water,  cool,  and  test  for 
starch. 

Make  the  same  tests  on  beets. 

Experiment  119. 

Materials : 
Orange. 
Apple. 

Test  some  of  the  orange  juice  and  some  of  the  apple  juice  for 
reducing  sugars.  Also  test  the  juices  with  litmus.  Test  the  pulp 
for  starch  by  boiling  with  water,  cooling,  and  adding  iodine. 

Experiment  120. 

Materials : 
Oatmeal. 
Beans,  ground. 
Walnuts,  ground. 

Test  each  for  starch  and  for  proteins.  Shake  a  portion  of  each 
with  benzine,  filter  through  a  dry  filter  on  to  a  clean  watch  glass, 
set  in  a  warm  place  to  evaporate  the  benzine.  If  a  residue  remains, 
add  Sudan  III  solution  and  warm  water.  What  do  you  infer  from 
the  result  ? 

Very  few  of  the  foods  of  vegetable  origin  contain  as  large 
a  proportion  of  proteins  as  is  demanded  by  the  older  "  dietary 
standards,"  which,  in  general,  require  15  to  16  Calories  out 
of  every  100  to  come  from  protein.  Reference  to  the  tables 
will  show  that  mushrooms,  peas,  beans,  peanuts,  butternuts, 
cocoa,  and  oatmeal  have  more  than  this  proportion  of  pro- 
tein. So  also  have  several  of  the  foods  known  as  "  vege- 
tables "  in  cookery  —  including  most  of  those  derived  from 
the  stalks  and  leaves  of  plants,  and  also  pumpkins,  tomatoes, 
and  radishes.  In  the  case  of  these  latter,  however,  it  is  to 


FOODS    OF    VEGETABLE    ORIGIN  211 

be  remembered  that  a  considerable  proportion  of  the  nitrogen 
calculated  as  protein  is  really  not  in  true  protein  compounds, 
and  that,  being  bulky  foods  containing  much  water,  these 
"  vegetables  "  do  not,  as  a  rule,  contribute  a  very  large  pro- 
portion of  the  total  fuel  value  of  the  diet. 

On  the  basis  of  the  more  recently  proposed  "  dietary 
standards  "  —  not  only  the  radically  low  protein  one  of 
Chittenden  but  also  the  more  moderate  standards  such  as 
that  of  Langworthy  1  —  a  much  larger  number  of  foods  of 
vegetable  origin  contain  an  adequate  proportion  of  proteins. 
These  would  include  wheat  flour  and  bread,  potatoes  and  most 
varieties  of  roots,  and  the  greater  number  of  varieties  of  nuts. 

As  a  rule  the  quantity  of  fat  in  vegetable  foods  is  small. 
Conspicuous  exceptions  are  the  nuts  (including  peanuts), 
chocolate  and  its  derivative  cocoa,  and  olives.  The  germs  of 
cereal  grains  are  also  rich  in  fat.  But  in  the  manufacture 
of  some  commercial  foods  from  cereals  —  particularly  in 
that  of  white  flour  and  cornmeal  —  the  germ  is  removed 
because  of  the  tendency  of  the  fat  to  become  rancid  and  thus 
cause  deterioration  of  the  product.  Oatmeal  and  rolled  oats, 
on  the  other  hand,  contain  fat  sufficient  to  yield  a  fuel  value 
equal  to  that  of  their  proteins,  and  are  thus  the  best  balanced 
of  all  the  cereal  products.  In  cooking  cereals  and  vegetables 
it  is  common  to  add  fat  to  compensate  for  the  natural  defi- 
ciency of  such  foods  in  this  nutrient.  Hence  the  division  of 
the  table  entitled  "  Baked  Foods  "  (pp.  274-5)  shows  in  many 
instances  a  liberal  proportion  of  fats  to  carbohydrates. 

As  to  the  quantities  of  the  important  mineral  elements  — 
calcium,  phosphorus  and  iron  —  that  they  contain,  foods  of 
vegetable  origin  differ  greatly.  Table  II  in  Appendix  A 
(pp.  278-9)  gives  the  quantities  of  these  three  elements  (the 
calcium  and  phosphorus  stated  in  terms  of  milligrams  of 
their  oxides,  the  iron  as  milligrams  of  the  element)  contained 
in  the  loo-Calorie  portion  of  a  number  of  vegetable  foods, 

1  Sherman's  "  Chemistry  of  Food  and  Nutrition,"  Chapter  VIII. 


212 


ELEMENTARY  HOUSEHOLD   CHEMISTRY 


classified  as  in  Table  I.  To  compare  the  foods  on  the  basis 
of  equal  weights,  one  must  divide  these  quantities  by  the 
weight  of  the  loo-Calorie  portion.  Thus,  while  per  100- 
Calorie  portion  spinach  is  much  richer  than  ripe  beans  in 
all  three  of  these  constituents,  it  is  much  poorer  in  all  per 
100  grams  or  per  pound. 


SPINACH 

BEANS 

i  oo-  Calorie  portion  in  grams  .  .  . 
CaO  per  100-  Calorie  portion  .  .  . 
CaO  per  100  grams  
P2OS  per  i  oo-  Calorie  portion  .  .  . 
P2Os  per  100  grams 

412 
370  mg. 
89  mg. 
540  mg. 

I  2Q  IH2T 

29 
63  mg. 
217  mg. 
336  mg. 
114.0  msr 

Fe  per  loo-Calorie  portion  .  .  . 
Fe  per  100  grams  

13-3  mg. 
•j  2  me 

2.0  mg. 
6  Q  me. 

Among  foods  of  its  own  class,  however,  spinach  stands 
conspicuously  high  as  regards  its  content  of  iron  and  phos- 
phorus and  fairly  high  also  as  regards  calcium.  Cauliflower 
and  celery,  however,  are  much  richer  in  calcium.  The  legumes 
are  also  rich  in  all  three  of  the  important  mineral  elements. 
Among  the  cereals,  those  containing  the  outer  layers  of  the 
grain  (oatmeal  and  Graham  flour)  are  richest  in  all  three  of 
these  elements. 

An  adequate  supply  of  the  bone-forming  materials,  lime 
and  phosphoric  acid,  is  of  special  importance  in  children's 
dietaries.  Table  II  shows  that  green  vegetables  and  roots 
(especially  turnips,  carrots,  and  parsnips)  are  conspicuously 
rich  in  these  ingredients.  Some  fruits  also  (for  example, 
oranges)  contain  much  calcium  in  the  form  of  organic  salts. 

As  noted  in  Chapter  XXXVI  (p.  200)  the  cereals  contain 
a  small  excess  of  acid-forming  constituents,  while  in  the  vege- 
tables, fruits,  and  legumes  base-forming  elements  predomi- 
nate. 


CHAPTER  XXXIX 

FOODS   OF  ANIMAL   ORIGIN 

IF  the  foods  of  vegetable  origin  are  to  be  regarded  as  mainly 
carbohydrate  foods,  those  of  animal  origin  are,  on  the  whole, 
to  be  regarded  as  protein  and  fat  foods.  To  be  sure,  honey 
contains  practically  no  nutrient  but  the  carbohydrates, 
glucose,  fructose,  and  a  little  sucrose ;  but  it  is  exceptional. 
Other  than  honey,  the  only  animal  foods  containing  any 
proportion  of  carbohydrates  worthy  of  consideration  are 
milk  and  some  of  its  products  (particularly  skim  milk,  butter- 
milk, and  whey),  and  shellfish,  such  as  oysters  and  clams. 
Liver,  cream,  cheese,  and  shad  roe  contain  minor  quantities 
of  carbohydrates.  All  the  other  animal  foods  are  made  up 
(as  regards  their  organic  nutrients)  almost  exclusively  of 
protein  and  fat. 

The  proportions  of  these  two  classes  of  nutrients,  protein 
and  fats,  vary  widely  in  the  different  animal  foods.  Egg- 
white  is  fat  free,  consisting  of  pure  protein  matter  with  some 
ash  and  much  water.  Gelatin  is  all  protein  also,  but,  curi- 
ously enough,  it  is  not  by  itself  capable  of  building  muscular 
tissue  —  a  fact  that  is  probably  related  to  the  absence  of 
certain  amino  acids  (particularly  tyrosine  and  tryptophane) 
from  among  its  hydrolysis  products.  The  protein  of  frogs' 
legs  and  of  codfish  yields  over  95  per  cent  of  the  total  fuel 
value  of  these  foods.  On  the  other  hand,  the  energy  of  fat 
pork,  of  cream,  and  of  butter  comes  nearly  all  from  the  fat ; 
and  lard  and  tallow  are,  of  course,  practically  pure  fats. 

Meats  vary  greatly  in  composition  with  the  variety,  the 
cut,  and  the  condition  of  the  animal  when  killed.  The 
tongue,  breast,  and  shoulder,  for  instance,  are  much  more 
muscular  than  the  ribs,  loin,  and  rump.  Hence  we  find  a 

213 


214  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

larger  proportion  of  protein  in  cuts  of  the  former  class,  and 
a  larger  proportion  of  fat  in  those  of  the  latter. 

Table  III  of  Appendix  A  (p.  280)  gives  the  average  com- 
position and  nutritive  value  of  several  varieties  and  cuts  of 
meats.  Table  IV  (p.  282)  illustrates  how  widely  the  same 
cuts  may  vary  according  as  they  are  from  fat  or  lean  ani- 
mals. The  figures  given  in  the  latter  table  are  not  the  ex- 
treme values  found  in  individual  cuts  of  meat,  but  are  in  each 
instance  the  average  of  the  results  of  analysis  of  several 
pieces  classed  as  fat,  medium  fat,  lean,  etc.  It  will  be 
observed  that  as  the  percentage  of  fat  in  the  meat  increases 
the  percentages  of  water  and  protein  decrease.  But  even 
the  leanest  meat  is  not  entirely  devoid  of  fat. 

Experiment  121. 

Materials : 
Lean  beef. 

Remove  all  visible  fat  from  the  beef ;  then  cut  it  up  into  fine 
pieces  or  put  it  through  a  mincer.  Place  some  of  the  minced  meat 
in  a  dish,  cover  with  alcohol,  and  knead  to  extract  the  water  from 
the  tissues.  Pour  off  this  alcohol,  add  more,  and  knead  again. 
Pour  off  the  alcohol,  add  benzine,  and  knead  or  shake.  Filter  off 
the  benzine,  allow  it  to  evaporate,  and  test  the  residue  for  fat  with 
Sudan  III  solution. 

Experiment  122. 

Materials  : 
Lean  beef. 

Mince  the  beef,  put  it  in  a  cheesecloth  bag,  and  knead  in  running 
water  until  the  tissues  are  white.  Apply  Millon's  test  and  the 
xanthoproteic  test  to  these  tissues. 

Reference  to  Table  III  (Appendix  A)  will  show  that  pork, 
mutton,  and  lamb  are,  as  a  rule,  fatter  than  beef,  and  beef  is 
usually  fatter  than  veal.  The  average  fore  quarter  or  hind 
quarter  of  beef  yields  out  of  every  100  Calories  about  30 
Calories  from  protein  and  70  Calories  from  fat.  The  fore 
quarter  or  hind  quarter  of  mutton  yields  about  20  Calories 


FOODS    OF   ANIMAL    ORIGIN  215 

from  protein  and  80  from  fat.  The  average  pork  ham  yields 
about  17  Calories  from  protein  to  83  from  fat,  and  the  average 
side  of  pork  only  7  Calories  from  protein  out  of  every  100. 
Average  veal,  on  the  other  hand,  has  about  half  of  its  fuel 
value  in  the  form  of  protein. 

When  the  fat  is  largely  trimmed  off  by  the  butcher  or 
cook  or  rejected  at  table,  there  is,  of  course,  not  only  a  great 
loss  of  fuel  value,  but  the  proportions  of  protein  and  fat  in 
the  food  actually  eaten  are  greatly  altered.  Rejected  fat 
is  not  included  in  the  refuse  as  estimated  in  the  tables. 
These  tables,  therefore,  give  higher  energy  values  to  the  meats 
than  are  usually  realized  from  them. 

Table  V  (Appendix  A,  p.  283)  gives  the  average  composi- 
tion and  nutritive  value  of  fish  of  several  varieties. 

Most  fish  have  over  half  their  fuel  value  in  the  form  of 
protein.  A  few  of  the  fatter  varieties,  such  as  sardines, 
salmon,  trout,  shad,  and  eels,  have  a  little  less  than  half 
(43  to  50  per  cent)  of  their  fuel  value  in  the  protein  form, 
while  the  leanest  varieties,  such  as  cod,  haddock,  and  pickerel, 
may  have  as  much  as  90  Calories  out  of  every  100  from 
protein. 

Table  VI  (Appendix  A,  p.  284)  gives  the  average  composi- 
tion and  fuel  value  of  dairy  products.  Here  a  column  must 
be  provided  for  the  carbohydrates,  viz.  the  lactose.  In  whole 
milk,  evaporated  milk,  and  milk  powder  this  provides  about 
29  per  cent  of  the  total  fuel  value.  In  the  dairy  products 
richer  in  fat  (butter,  cream,  and  cheese)  the  lactose  plays  a 
minor  part.  In  skim  milk,  buttermilk,  and  whey,  on  the 
other  hand,  it  becomes  the  most  prominent  nutrient.  In 
sweetened  condensed  milk  the  cane  sugar  added  constitutes 
about  four  fifths  of  the  total  carbohydrates  and  the  milk 
sugar  only  one  fifth. 

Table  VII  (Appendix  A,  p.  285)  gives  the  composition  and 
nutritive  value  of  miscellaneous  foods  of  animal  origin.  Eggs, 
it  will  be  noted,  are  protein  and  fat  foods.  The  whites,  how- 


2l6  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

ever,  contribute  protein  only,  while  the  yolks  have  twice 
as  much  fat  as  protein  by  weight  and  between  four  and  five 
times  as  much  by  calories.  Shad  roe  and  the  shellfish,  in 
spite  of  the  presence  of  carbohydrates  (glycogen),  are  highly 
nitrogenous  foods.  The  shellfish,  white  of  eggs,  and  frogs' 
legs  have  high  loo-Calorie  portions  on  account  of  their  high 
water  content  and  low  fat  content.  In  other  words,  although 
their  dry  matter  is  highly  nitrogenous,  they  contain  only  a 
small  amount  of  dry  matter  per  pound. 

Meats  are  poor  in  calcium,  and  eggs  contain  only  a  moderate 
amount.  See  Table  VIII  (Appendix  A,  p.  286).  Milk,  how- 
ever, is  extraordinarily  rich  in  this  element,  and  the  same  is 
true  of  some  of  its  products,  especially  cheese  and  buttermilk. 
As  pointed  out  by  Sherman,  a  quart  of  milk  contains  rather 
more  calcium  than  a  quart  of  clear,  saturated  limewater, 
and  one  would  need  to  take  25  hundred-Calorie  portions  of 
round  steak  and  white  bread  to  get  as  much  calcium  as  one 
could  obtain  in  i  hundred-Calorie  portion  of  whole  milk  or 
of  cheese. 

The  majority  of  animal  foods  contain  a  liberal  supply 
of  phosphorus.  In  egg  yolk  this  exists  in  the  form  of  phos- 
phorized  fats  and  phospho-proteins  —  forms  in  which  it  is 
more  readily  assimilated  than  in  the  inorganic  phosphates. 
In  meat  and  fish  it  is  mainly  in  the  inorganic  forms.  In  milk 
it  is  present  in  both  inorganic  and  organic  forms ;  in  cheese, 
chiefly  in  organic  combination,  viz.  as  casein. 

Iron  in  readily  assimilable  form  is  abundant  in  egg  yolk. 
It  is  from  the  organic  iron  compounds  contained  in  the  yolk 
that  the  hemoglobin  of  the  chick's  blood  is  formed,  and  there 
is  good  reason  to  believe  that  it  serves  a  similar  purpose  in 
the  human  diet.  The  iron  in  lean  meats  is  chiefly  present  as 
hemoglobin  in  the  blood  retained  in  the  tissues.  It  is,  how- 
ever, not  certain  that  this  iron  is  as  useful  in  the  human  diet 
as  that  of  eggs,  milk,  and  vegetables,  because  hemoglobin 
is  not  readily  digested. 


>   FOODS    OF   ANIMAL   ORIGIN  217 

Milk  and  eggs  are  especially  valuable  foods  for  children, 
not  only  on  account  of  their  protein  content  and  the  emulsi- 
fied condition  of  their  fats,  but  also  on  account  of  the  kinds 
of  mineral  matter  they  contain.  Per  loo-Calories  of  fuel 
value  milk  contains  far  more  calcium  than  any  other  food. 
It  is  also  rich  in  phosphorus,  being  surpassed,  however,  in 
this  respect  by  a  few  foods,  such  as  lean  beef  and  beans. 
Eggs  are  also  among  the  richest  foods  in  phosphorus  content, 
and  contain  a  fair  proportion  of  calcium  as  well. 


CHAPTER  XL 

TEXTILE  FIBERS  OF  ANIMAL  ORIGIN.    WOOL  AND 

SILK 

TEXTILES  for  clothing  and  for  household  furnishings  can 
be  made  from  any  kind  of  fiber,  natural  or  artificial,  which 
has  sufficient  length,  strength,  and  elasticity.  The  mineral 
kingdom  furnishes  some  such  fibers  —  asbestos,  spun  gold 
and  silver,  and  spun  glass.  On  account  of  their  costliness 
and  other  defects,  however,  the  mineral  fibers  find  only 
limited  application.  Both  the  vegetable  and  the  animal 
kingdoms,  on  the  other  hand,  yield  us  fibers  of  very  wide 
utility. 

The  animal  fibers  are  of  two  classes,  viz.  (i)  Hair  fibers, 
of  which  wool  is  by  far  the  most  important ;  (2)  Silk  fibers. 
Both  classes  are  composed  of  protein  substances,  but  the 
silks  are  sulphur-free,  while  the  hair-fibers,  being  keratins, 
are  rich  in  sulphur.  (See  Expt.  112,  p.  191.) 

Experiment  123. 

Materials : 
Wool. 
Silk. 

Burn  a  little  of  each  kind  of  fiber  in  a  flame,  noting  the  odor  and 
the  shape  which  the  end  of  the  fiber  assumes.  Heat  portions  in 
small,  dry  test  tubes  and  test  the  evolved  gases  for  ammonia  with 
red  litmus  paper,  and  for  hydrogen  sulphide  gas,  H2S,  with  paper 
moistened  with  lead  acetate  solution.  Hydrogen  sulphide  reacts 
with  lead  acetate  to  give  lead  sulphide,  PbS,  which  is  black. 

Make  the  xanthoproteic  test  (Expt.  105,  p.  186)  and  Millon's 
test  (Expt.  106,  p.  187)  on  other  portions  of  the  wool  and  silk. 

218 


FlG    42  _  w00i  fibers  magnified.  FIG.  43.  —  Silk  fibers  magnified. 

From  Kinne  and  Cooky's  "  Shelter  and  Clothing,"       From  Kinne  and  Cooley's  "  Shelter  and  Clothing,? 
by  kind  permission .  by  kind  permission. 


FIG.  44.  —  Cotton  fibers  magnified.  FIG.  45.  — Flax  fibers  magnified. 

From  Kinne  and  Cooley's  "  Shelter  and  Clothing,"     From  Kinne  and  Cooley's  "  Shelter  and  Clothing,' 

by  kind  permission.  by  kind  permission. 


TEXTILE    FIBERS    OF    ANIMAL    ORIGIN  219 

Experiment  124. 

Materials  : 
Silk  fibers. 
Wool. 

Human  hair. 
Cat's  hair. 
Apparatus : 

Microscope  and  slides. 

Examine  the  fibers,  noting  points  of  similarity  among  the  various 
hair  fibers  and  differences  of  these  from  the  silk.  Observe  partic- 
ularly the  scaly  surface  of  the  hair  fibers.  Is  there  any  noticeable 
difference  between  wool  and  the  coarser  hair  fibers  in  regard  to 
(a)  diameter,  (b)  appearance  of  the  scales  ? 

Wool 

A  hair  fiber  comprises  three  distinct  portions:  (i)  the 
medulla,  a  cellular  marrow,  which  frequently  contains  the 
pigment  to  which  the  wool  owes  its  color;  (2)  the  fibrous 
cortical  tissue,  to  which  the  fiber  owes  most  of  its  strength 
and  elasticity;  (3)  the  epidermis  of  horny  scales,  consisting 
of  flattened  cells,  overlapping  one  another  like  shingles. 

The  characteristics  which  distinguish  wool  from  other  hair 
fiber  are  its  fineness,  its  softness,  and  the  abundance  of  its 
scales  or  serrations.  To  these  scales  is  due  the  characteristic 
"  felting  "  property  of  wool ;  that  is  to  say,  the  tendency  of 
the  fibers  to  mat  together,  and  also  the  tendency  of  woolen 
goods  to  shrink,  the  scales  catching  upon  one  another  and 
so  preventing  the  fibers  returning  to  their  original  position. 

The  length  and  fineness  of  wool  depend  chiefly  upon  the  breed 
of  sheep  producing  it,  but  these  qualities,  as  well  as  the  strength 
and  luster,  are  influenced  also  by  the  climate  in  which  the  sheep 
are  grown,  by  the  nature  of  the  soil  providing  the  pasture,  and  by 
the  condition  of  the  animals'  health.  Ordinarily,  the  length  of 
the  fibers  is  between  i  and  8  inches  and  the  diameter  between  ifa 
and  T^t  inch.  The  quality  of  the  wool  varies  not  only  in  different 
fleeces,  but  also  in  the  different  parts  of  the  same  fleece,  the  wool  of 
the  shoulders  and  sides  excelling  in  length,  strength,  and  uniformity, 


220  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

while  that  from  the  upper  parts  of  the  legs  is  coarse  and  that  from 
the  head,  chest,  and  lower  parts  of  the  legs  is  likely  to  be  coarse, 
stiff,  and  dirty.  The  uses  of  the  wool  depend  upon  its  quality, 
which  in  turn  depends  upon  such  physical  properties  as  the  length, 
diameter,  strength,  elasticity,  and  glossiness  of  the  fibers. 

Only  the  longer  and  brighter  fibers,  for  instance,  are  suitable 
for  the  manufacture  of  worsteds.  The  wool  manufacturer  grades 
and  sorts  his  wool  and  uses  the  different  kinds  for  the  manufacture 
of  different  classes  of  goods. 

Raw  wool  contains  a  large  proportion  of  impurities.  In 
some  merino  wools  these  impurities  constitute  as  much  as 
70  per  cent  of  the  total  dry  weight  of  the  fleece.  The  im- 
purities consist  of : 

(a)  Wool  grease,  a  fatty  substance,  which  serves  as  a  protective 
covering  to  the  fibers. 

(b)  Suint,  that  is,  dried  perspiration,  consisting  chiefly  of  potas- 
sium soaps. 

(c)  Vegetable  matter,  such  as  burrs,  straw,  and  vegetable  fibers 
from  sacks  and  twine. 

(d)  Mineral  matter,  such  as  clay. 

Unwashed  wool  contains  from  4  to  24  per  cent  of  moisture; 
from  12  to  47  per  cent  of  yolk  (grease  and  suint) ;  from  3  to  24 
per  cent  of  dirt ;  and  from  15  to  72  per  cent  of  true  wool  fiber. 

Wool  grease,  the  chief  constituent  of  which  is  an  alcohol,  called 
cholesterol,  is  the  source  of  a  product  known  as  lanolin.  Lanolin 
has  remarkable  capacity  for  forming  emulsions  with  water  and 
aqueous  solutions,  and  is  readily  absorbed  by  the  skin.  On  this 
account  it  is  used  in  many  pharmaceutical  ointments  and  cosmetics. 

The  impurities  are  removed  from  the  wool  by  "  scouring," 
that  is,  washing  with  soap  and  an  alkali.  Only  the  milder 
alkalies,  such  as  the  carbonates  of  potassium  and  sodium, 
ammonia  or  borax,  may  be  used,  not  the  caustic  alkalies. 
By  this  treatment  the  soaps  in  the  wool  are  dissolved,  the 
fats  are  emulsified  and  removed  from  the  wool  fibers,  and  the 
earthy  matters  are  thereby  loosened  and  washed  out.  Much 
of  the  vegetable  matter,  however,  remains  in  the  wool  and 
is  removed  by  subsequent  treatment.  In  the  worsted  pro- 


TEXTILE    FIBERS    OF    ANIMAL    ORIGIN  221 

cess  this  subsequent  treatment  is  simply  a  combing,  which 
removes  not  only  the  vegetable  matter,  but  also  those  wool 
fibers  which  are  too  short  to  be  used  in  worsted  yarns.  In 
the  manufacture  of  woolens,  where  these  shorter  wool  fibers 
are  used,  the  vegetable  matter  is  removed  by  a  chemical 
process  known  as  carbonizing. 

Carbonizing. — The  washed  wool  is  treated  with  dilute 
sulphuric  acid  (sp.  gr.  1.03)  and  then  subjected  to  a  temper- 
ature of  140°  to  180°  F.  (60-80°  C.),  at  which  temperature 
the  vegetable  matter  is  rendered  brittle  by  the  conversion  of 
the  cellulose  into  hydrocellulose.  The  brittle  residue  is  then 
shaken  out  of  the  wool,  and  the  sulphuric  acid  is  neutralized 
with  soda  and  washed  out. 

With  the  exception  of  the  bleaching  and  dyeing,  which  will 
receive  consideration  later  (Chapters  XLII  and  XLIII),  the 
remaining  operations  of  the  woolen  industry  —  the  carding, 
spinning,  weaving,  and  finishing  —  involve  no  chemistry,  but 
are  purely  mechanical.1 

Experiment  125. 

Material: 

Scoured  wool  or  woolen  yarn. 

Weigh  the  wool  (about  5  grams)  on  a  balance  accurate  in  the 
second  decimal  place.  Dry  for  one  hour  in  a  water  oven.  Remove 
from  the  oven,  place  in  a  corked  test  tube,  the  weight  of  which 
has  previously  been  determined,  and  as  soon  as  the  wool  is  cool, 
weigh  again.  Reheat  for  half  an  hour,  weigh  again,  and  repeat 
until  the  wool  ceases  to  lose  weight.  Calculate  the  percentage 
of  moisture.  The  wool  should  be  allowed  to  cool  in  dry  air.  If 
a  desiccator  —  i.e.  an  apparatus  in  which  air  is  kept  dry  by  ex- 
posure to  sulphuric  acid  or  calcium  chloride — is  at  hand,  the  wool 
may  be  placed  in  it. 

Dry  wool  absorbs  moisture  from  the  air.  Substances 
which  do  this  are  said  to  be  hygroscopic.  Dry  wool  is  capable 
of  taking  up  an  average  of  16  per  cent  of  its  own  weight  of 

1  For  a  description  of  these  processes  the  reader  is  referred  to  Woolman  and 
McGowan's  "  Textiles."  (See  p.  228.) 


222  ELEMENTARY   HOUSEHOLD    CHEMISTRY 


water  from  ordinary  air,  while  cotton  absorbs  only  8  or  8j 
per  cent  of  its  weight.  The  amount  of  hygroscopic  moisture 
in  wool  at  any  given  time  depends  upon  the  humidity  of  the 
atmosphere  to  which  it  has  been  exposed. 

In  addition  to  the  hygroscopic  water,  which  is  condensed 
on  the  surface  of  the  fibers,  wool  contains  some  water  chemi- 
cally combined  with  the  protein  compounds.  Such  water 
is  known  as  "  water  of  hydra tion."  When  in  the  manu- 
facture or  subsequent  treatment  of  woolen  goods  the  water 
of  hydra  tion  is  driven  off  by  overheating,  the  luster  and 
strength  of  the  fibers  are  irrecoverably  lost.  In  pressing 
wool  goods,  therefore,  care  must  be  taken  to  avoid  subjecting 
them  to  dry  heat. 

Experiment  126.  —  Action  of  Acids. 

Material : 

White  woolen  yarn. 

Treat  wool  with  (a)  dilute  sulphuric  acid,  (&)  concentrated 
sulphuric  acid,  (c)  dilute  hydrochloric  acid,  (d)  concentrated  hydro- 
chloric acid,  (e)  concentrated  nitric  acid.  If  no  action  occurs  in 
the  cold,  heat  the  acid.  Which  of  the  acids  affects  wool?  Can 
you  account  for  the  effect  of  the  nitric  acid  ?  Neutralize  the  nitric 
acid  solution  with  ammonia  and  note  effect  on  color. 

Experiment  127.  — Action  of  Alkalies. 

Treat  white  wool  yarn  with  (a)  sodium  hydroxide  solution, 
cold  (allow  to  stand  several  hours)  ;  (b)  sodium  hydroxide, 
boiling;  (c)  sodium  carbonate,  boiling;  (d)  borax,  boiling; 
(e)  ammonia. 

Where  the  yarn  is  not  destroyed,  pour  off  the  reagent,  rinse 
with  water,  and  compare  the  strength  of  the  treated  yarn  with 
that  of  a  piece  of  the  same  yarn,  untreated. 

Wool  is  not  affected  by  dilute  acids,  but  is  very  sensitive 
to  alkalies,  which,  it  will  be  remembered,  readily  attack 
most  proteins.  Soap  containing  free  alkali  should  therefore 
be  avoided  in  washing  woolen  goods.  The  free  alkali  dis- 
solves off  the  scales  and  renders  the  fibers  hard  and  weak. 


TEXTILE    FIBERS    OF    ANIMAL    ORIGIN  223 

Soda  (sodium  carbonate),  if  free  from  caustic  soda,  is  less 
harmful  than  soap  containing  caustic  soda  (free  alkali). 
But  soda  is  not  without  a  certain  amount  of  effect.  Am- 
monia, borax,  and  neutral  soap  are  permissible  alkalies  for 
the  washing  of  woolen  goods. 

Silk 
Experiment  128. 

Material : 

Silk. 
Apparatus : 

Microscope. 

Examine  silk  fibers  under  the  microscope,  comparing  them  with 
wool  and  hair  fibers,  as  regards  fineness  and  structure. 

Silk  is  obtained  from  the  cocoons  of  a  species  of  cater- 
pillar, which  feeds  upon  the  leaves  of  the  mulberry  tree.  In 
making  silk  the  silkworm  secretes  a  viscous  liquid,  fibroin, 
in  two  glands  in  its  body,  and  forces  this  liquid  through  two 
minute  channels  in  its  head  into  a  single  exit  tube.  Two 
other  glands  deliver  into  the  same  tube  a  cementing  fluid, 
known  as  sericin.  As  it  emerges  from  the  head  of  the  worm 
the  fibroin  coagulates,  thus  forming  a  double  thread  cemented 
with  sericin. 

Besides  the  silkworm  proper  there  are  other  kinds  of  cater- 
pillars which  produce  silk.  Since  these  latter  worms  are  not 
cultivated  by  man,  as  are  the  mulberry  silkworms,  their  products 
are  known  as  wild  silks.  The  best-known  wild  silk  is  tussah  (or 
tussur)  silk  used  in  the  manufacture  of  pongee.  The  wild  silk 
fibers  are  coarser  and  hence  stronger,  but  more  broken  than  those 
of  the  mulberry  silkworm.  They  are  also  commonly  dark  in 
color  and  hard  to  bleach.  Wild  silks  find  use  in  the  manufacture 
of  pile  fabrics,  such  as  velvet,  plush,  and  imitation  sealskin. 

The  true  silk  fiber  is  notable  for  its  great  length  and  ex- 
treme fineness.  The  cocoon  threads  are  only  .0005  to  .0007 


224  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

inch  in  diameter  (1430  to  2000  threads  in  the  inch),  but  the 
length  may  be  as  much  as  1300  to  1400  yards.  Silk  is  also 
distinguished  by  its  high  luster  and  by  its  great  strength  and 
elasticity. 

About  75  per  cent  of  the  weight  of  the  raw  silk  is  fibroin, 
the  fiber  proper,  and  25  per  cent  the  cementing  substance, 
sericin,  also  known  as  silk  gum  or  silk  glue.  Both  fibroin 
and  sericin,  although  sulphur-free,  behave  like,  and  are 
classed  as,  proteins.  Sericin,  however,  is  soluble  in  hot 
water  and  forms  a  jelly  on  cooling.  In  this  respect  it  closely 
resembles  gelatin,  hence  the  name  "  silk  gelatin  "  sometimes 
applied  to  it.  In  the  manufacture  of  silk  more  or  less  of  the 
sericin  is  removed  by  treatment  with  hot  soap  solution,  the 
process  being  known  as  boiling  of,  stripping,  or  degumming. 

Ecru  silk  is  silk  which  has  lost  2  to  5  per  cent  of  its  total  weight, 
i.e.  Y5-  to  -5-  of  its  sericin,  in  boiling  off. 

Souple  silk  is  that  which  has  lost  12  to  14  per  cent  of  its  weight, 
i.e.  about  half  its  sericin. 

Boiled-o/  silk  is  that  which  has  lost  22  to  25  per  cent  of  its 
weight,  i.e.  practically  all  its  sericin. 

Silk  is,  like  wool,  a  hygroscopic  substance.  Under  fa- 
vorable atmospheric  conditions  raw  silk  will  absorb  as  much 
as  30  per  cent  of  its  weight  of  moisture  without  appearing 
wet.  Boiled-off  silk  is,  however,  much  less  hygroscopic. 
Ordinarily,  air-dry  silk  contains  about  10  to  12  per  cent  of 
moisture,  and  it  is  the  custom  in  the  trade  to  buy  and  sell 
silk  on  the  basis  of  its  perfectly  dry  weight  plus  n  per  cent ; 
in  other  words  the  quantity  of  silk  which  when  perfectly 
dried  weighs  100  pounds  is  sold  as  in  pounds  of  silk. 

Experiment  129. 

Weigh  about  5  grams  silk.  Dry  in  oven  at  100°  C.  to  constant 
weight,  as  in  Experiment  125.  What  would  be  the  legal  weight 
of  this  piece  of  silk  ? 


TEXTILE    FIBERS    OF    ANIMAL    ORIGIN  22$ 

Experiment  130.  — Action  of  Acids. 

Material : 
White  silk  thread. 

Treat  silk  thread  with  acids,  as  in  Experiment  126,  and  either 
compare  with  the  results  obtained  on  wool  in  that  experiment  or 
make  the  experiments  on  wool  and  silk  in  parallel.  Compare  the 
rates  of  solution  in  concentrated  nitric  acid.  Note  particularly  the 
difference  in  the  effect  of  cold  concentrated  hydrochloric  acid  on 
the  two  materials.  The  violet  coloration  produced  by  the  action 
of  concentrated  hydrochloric  acid  on  boiling  or  long  standing  is 
one  of  the  characteristic  reactions  of  proteins. 

Experiment  131.  — Action  of  Alkalies. 

Make  experiments  on  silk  parallel  to  those  of  Experiment  127. 
Which  of  the  two  materials  is  the  more  susceptible  to  the  action 
of  alkalies?  Which  to  the  action  of  acids? 

Experiment    132. — Action     of    Basic    Zinc    Chloride    (Eisner's 

Reagent x). 

Heat  Eisner's  reagent  to  boiling.  Tie  a  silk  thread  on  to  a  glass 
rod  and  dip  into  the  hot  liquid.  Make  the  same  experiment  with 
a  piece  of  woolen  yarn. 

The  above  experiments  suggest  methods  of  quantitatively 
determining  the  proportion  of  silk  in  a  mixed  fabric  of  wool 
and  silk.  The  silk  may  be  dissolved  out  with  either  con- 
centrated hydrochloric  acid  or  boiling  basic  zinc  chloride, 
and  the  un dissolved  residue  of,  wool  washed,  dried,  and 
weighed. 

The  Weighting  of  Silk 

Silk  absorbs  and  combines  with  the  tannins  or  tannic 
acids,  —  organic  substances  contained  in  various  plants  and 
used  in  tanning  leather, — and  the  tannins,  in  turn,  react  with 
iron  salts,  giving  dark-colored  dye  products.  By  successively 
treating  silk  with  'an  iron  salt  and  a  tannin  the  weight  of  the 

1  Dissolve  500  grams  zinc  chloride  and  20  grams  zinc  oxide  in  425  cc.  water, 
warming  till  clear.     The  liquid  becomes  turbid  on  standing  in  the  cold,  but 
clears  again  on  heating. 
Q 


226  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

fibers  can  be  greatly  increased.  Sometimes  potassium  or 
sodium  ferrocyanide  is  used  in  place  of,  or  in  addition  to, 
the  tannin.  Ferrocyanides  and  ferric  salts  react  together  to 
form  Prussian  blue,  an  insoluble  substance  which  precipi- 
tates in  the  fibers.  Thus : 

Ferric     ,         Sodium  Ferric  ,      Sodium 

nitrate    " "    ferrocyanide    " "    ferrocyanide  nitrate 

(Prussian  blue) 

Experiment  133. 

Materials : 

Tannin  of  gallnuts. 
Cutch  (catechu). 

Infuse  10  grams  of  each  of  the  tannin  materials  separately  with 
100  cc.  water.  Filter. 

In  test  tubes  mix  solutions  of :  (a)  Ferric  chloride  and  gallnut 
tannin  (gallotannic  acid),  (b)  Ferric  chloride  and  cutch  infusion 
(containing  catechutannic  acid),  (c)  Ferric  chloride  and  potassium 
ferrocyanide. 

Dilute  the  dark  products  until  you  can  see  through  the  liquid. 
In  which  instance  is  a  precipitate  formed  ? 

Experiment  134. 

Materials : 
Cutch. 

Ferric  nitrate  or  ferric  acetate. 
Piece  of  woven  ecru  silk. 

Infuse  10  grams  cutch  with  100  cc.  water.  Dissolve  10  grams 
ferric  nitrate  in  100  cc.  water.  Weigh  the  piece  of  silk  (i  to  2 
grams).  Heat  the  ferric  nitrate  solution  to  70-80°  C.  and  immerse 
the  silk  in  it  for  10  minutes.  Squeeze  out,  transfer  to  the  cutch 
bath,  and  heat  to  boiling.  Repeat  the  treatment  with  ferric 
nitrate  and  that  with  cutch  several  times.  Rinse  with  hot  water, 
dry,  and  weigh.  If  heat  is  applied  in  drying,  allow  the  silk  to 
stand  in  the  room  for  a  few  hours  before  weighing.  Calculate 
the  percentage  gain  in  weight. 

A  few  crystals  of  stannous  chloride  added  to  the  cutch  bath 
may  produce  a  greater  gain  of  weight. 

Weighting  with  iron  compounds  is  only  practicable  where 
the  silk  is  to  be  dyed  black  or  a  dark  color.  For  white  and 


TEXTILE    FIBERS   OF   ANIMAL   ORIGIN  227 

light-colored  silks  soluble  substances  such  as  sugar,  glucose, 
and  magnesium  chloride  were  formerly  and  are  still  some- 
times used,  but  the  most  successful  weighting  materials  are 
insoluble  compounds  of  tin.  Tin  silico-phosphate  is  one  of 
the  most  common  of  these  weighting  materials  for  light- 
colored  silk.  It  is  obtained  by  treating  the  goods  first  with 
stannic  chloride,  then  with  sodium  phosphate,  and  finally 
with  sodium  silicate. 

Experiment  135. 

Materials : 
Ecru  silk. 

Stannic  chloride  crystals  (or  anhydrous  stannic  chloride). 
Disodium  phosphate  crystals. 
Sodium  silicate  (or  water-glass  solution). 

Dissolve  40  grams  stannic  chloride  crystals  (SnCU  .  5  H2O)  or 
30  grams  (13  cc.)  anhydrous  stannic  chloride  in  70  cc.  of  water. 
Dissolve  13  grams  sodium  phosphate  crystals  (Na2HPO4 .  12  H2O) 
in  87  cc.  water.  Dilute  water-glass  solution  to  a  specific  gravity 
of  1.04. 

Weigh  a  piece  of  ecru  silk  (i  or  2  grams).  Place  it  in  the  stan- 
nic chloride  solution  and  let  stand  one  hour.  Heat  the  sodium 
phosphate  solution  and  the  sodium  silicate  solution  to  60°  C. 
(140°  F.).  Remove  the  silk  from  the  stannic  chloride,  rinse  it 
with  water,  and  immerse  in  the  sodium  phosphate  solution  for  10 
minutes,  then  in  the  sodium  silicate  for  the  same  length  of  time. 
Rinse,  dry,  and  weigh. 

The  process  may  be  repeated  five  or  six  times,  the  weight  in- 
creasing with  each  treatment. 

Compare  the  weighted  silk  with  an  untreated  piece  of  the  same 
goods,  noting  particularly  the  relative  strength  of  the  fibers. 

Burn  a  thread  of  heavily  weighted  and  a  thread  of  unweighted 
silk.  What  differences  of  behavior  are  observed? 

Silk  experts  maintain  that  moderate  weighting  —  up  to 
about  25  per  cent  of  the  weight  of  the  boiled-off  silk  —  is  not 
injurious,  but  rather  improves  the  wearing  quality  of  the  silk. 
Indeed,  the  term  "  pure  silk  "  is  used  in  the  trade  to  designate 
a  silk  which  has  been  weighted  just  sufficiently  to  compensate 


228  ELEMENTARY   HOUSEHOLD    CHEMISTRY 

for  the  loss  of  weight  sustained  in  boiling  off.  It  is  generally 
agreed,  however,  that  excessive  weighting  is  very  injurious. 
Goods  weighted  with  tin  compounds  are  especially  liable 
to  deterioration  on  exposure  to  air  and  light.  It  is  thought 
that  this  may  be  due  to  the  hydrolytic  effect  of  moisture  on 
the  stannic  chloride  retained  in  the  fibers.  Such  hydrolysis 
would  liberate  hydrochloric  acid,  which,  as  we  have  seen,  has 
a  solvent  action  on  silk.  Proceeding  on  this  assumption,  some 
manufacturers  treat  tin-weighted  goods  with  mildly  basic 
organic  compounds,  and  this  is  said  to  mitigate  the  evil  to 
some  extent  at  least. 

The  most  satisfactory  methods  of  estimating  the  amount  of 
weighting  in  silk  are : 

(1)  Treatment  with  dilute  hydrofluoric  acid,  which  dissolves 
the  weighting  without  affecting  the  silk. 

(2)  Determination  of  the  amount  of  nitrogen  in  the  material 
after  first  freeing  it  from  nitrogenous  weighting  materials,  such 
as  Prussian  blue,  ammonium  phosphate,  glue,  and  gelatin.     Since 
pure  boiled-off  silk  containing  n  per  cent  of  moisture  contains 
17.6  per  cent  of  nitrogen,  every  gram  of  nitrogen  found  in  the 
weighted  goods  represents  100-7-17.6  =5.68  grams  of  air-dry  silk. 
The  difference  between  the  original  air-dry  weight  and  the  esti- 
mated air-dry  weight  of  real  silk  represents  the  weight  of  the 
filling  material. 

(3)  Burning  the  goods  and  weighing  the  ash.     This  is  a  simple 
method  which  gives  good  results  with  light-colored  goods.     Un- 
weighted silk  leaves  less  than  i  per  cent  61  its  weight  of  ash. 
Silk    legitimately  weighted  leaves  not  over  25  per  cent.     Silks 
yielding  more  than  25  per  cent  of  ash  are  overweighted.     In  the 
case  of  black  goods  the  amount  of  weighting  may  considerably 
exceed  the  amount  of  ash,  since  spme  of  the  weighting  substances, 
e.g.  tannin,  are  combustible. 

For  an  account  of  the  silk  industry  and  of  the  properties  of  silk  fibers  and 
fabrics  which  should  influence  their  selection  and  use,  reference  may  be  made  to 
Woolman  and  McGowan's  "Textiles:  A  Handbook  for  the  Student  and  the 
Consumer"  (New  York,  1913)- 


CHAPTER  XLI 

TEXTILE  FIBERS    OF    VEGETABLE    ORIGIN.      COT- 
TON,  LINEN,   AND   ARTIFICIAL   SILK 

VEGETABLE  fibers  are  of  great  variety  if  we  include  such 
materials  as  are  used  in  the  manufacture  of  furniture  and 
floor  coverings  —  twigs,  canes,  rushes,  grasses,  leaf  fibers 
(e.g.  manila,  sisal),  etc.  Leaving  these  coarse  materials 
out  of  consideration,  the  natural  vegetable  fibers  resolve 
themselves  into  two  classes : 

(1)  Seed  hairs,   of  which  cotton  is  the  only  important 
example. 

(2)  Bast  fibers,  including  linen,  ramie,  jute,  and  hemp. 
Artificial  silks  (lustracelluloses)  are  artificial  fibers  made 

from  vegetable  materials. 

All  these  materials  are  carbohydrate  in  composition  and 
all  belong  to  that  class  of  carbohydrates  known  as  celluloses. 
Between  the  cellulose  of  cotton  and  that  of  linen  there  is 
little,  if  any,  difference. 

Wood-pulp  paper  and  jute  consist  of  lignocellulose,  a  dis- 
tinctly different  substance  from  true  cellulose.  Hemp  prob- 
ably contains  both  these  kinds  of  cellulose. 

Cotton 

Cotton  fibers  are  the  seed  hairs  of  several  varieties  of  the 
cotton  plant  (genus,  Gossypium),  most  species  of  which  grow 
as  shrubs  in  warm  climates. 

The  seed  hairs  are  inclosed  with  the  seed  in  a  sort  of  pod, 
known  as  a  boll.  The  bolls  are  harvested  when  they  burst 
open,  exposing  the  ripe  cotton. 

229 


230  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Experiment  136. 

Examine  cotton  fibers  under  the  microscope  at  a  magnifica- 
tion of  about  150  to  300.  Note  the  ribbon-like  form  and  the 
characteristic  twist.  Under  a  higher  magnification  (about  700) 
note  the  inner  canal  of  the  fiber. 

Cotton  fibers  (or  staple,  as  they  are  technically  termed) 
of  American  growth  vary  in  length  from  f  inch  in  Texas  to 
i \  inches  in  Uplands,  and  in  diameter  from  -jinnr  to  nnny  mcn> 
the  longer  fibers  having  the  smaller  diameters. 

They  are,  accordingly,  comparable  in  diameter  with  silk 
and  fine  wool,  but  much  shorter  than  either  silk,  wool,  or 
linen  fibers.  (See  pp.  223,  219  and  236).  Sea  Island  cotton, 
originally  grown  in  the  West  Indies,  and  Egyptian  cotton, 
which  has  been  developed  from  Sear  Island  stock,  have  a 
longer  staple  and  are  finer  than  that  from  the  American 
mainland.  It  is  this  finer  variety  of  cotton  which  is  em- 
ployed in  the  manufacture  of  mercerized  lawns. 

Cotton  fibers  consist  of  a  single  cell,  the  structure  of  which 
is  represented  in  Figure  44.  During  growth  the  interior 
tube  (lumen)  is  filled  with  a  liquid,  and  the  fiber  is  cylindrical. 
On  ripening,  the  liquid  withdraws  and  the  fiber  flattens  irregu- 
larly into  a  twisted  ribbon.  The  twist  is  not  only  a  valu- 
able mark  of  identification  of  cotton  fibers,  but  is  also  of 
great  practical  importance  in  facilitating  spinning.  As  a 
means  of  interknitting  the  fibers  it  plays  a  part  similar  to 
that  played  by  the  epidermal  scales  in  wool.  Raw  cotton 
fibers  have  300  to  500  twists  per  inch. 

The  raw  fiber  is  mixed  with,  and  attached  to,  the  cotton 
seed.  The  seed  is  removed  by  mechanical  processes  (gin- 
ning) —  not,  however,  without  some  injury  to  the  fibers. 
A  waxy  coating  also  covers  the  fiber.  The  quantity  of  wax 
is  small  —  usually  between  0.3  and  0.5  per  cent.  After 
the  cotton  is  spun,  this  wax  is  removed  by  boiling  the  cotton 
6  or  8  hours  in  a  dilute  (i  per  cent)  solution  of  caustic  soda 
under  slight  pressure.  The  bleaching  of  cotton  is  not  under- 
taken until  the  wax  has  been  removed. 


TEXTILE   FIBERS  OF  VEGETABLE  ORIGIN         231 

Chemical  Behavior 

Boiled-off  cotton  is  practically  pure  cellulose.  To  most 
reagents  cellulose  is  much  more  resistant  than  the  protein 
substances  which  constitute  the  animal  fibers. 

Experiment  137.  —  Action  of  Acids. 

Treat  wisps  of  absorbent  cotton  in  test  tubes  with  (a)  concen- 
trated sulphuric  acid,  (b)  concentrated  hydrochloric  acid,  (c)  con- 
centrated nitric  acid,  allowing  it  to  stand  in  the  cold  for  5  or  10 
minutes.  Afterwards  heat  tubes  (6)  and  (c).  Cool  tube  (c)  and 
neutralize  the  nitric  acid  with  ammonia.  Record  the  effect  of  each 
of  the  three  acids,  and  compare  with  the  effects  on  wool  and  silk. 
How  could  the  results  be  utilized  to  distinguish  (i)  cotton  from 
wool  and  silk,  (2)  cotton  and  wool  from  silk? 

Experiment  138.  — Action  of  Acids. 

Immerse  two  pieces  of  woven  cotton  goods  for  a  few  minutes 
in  dilute  sulphuric  acid  and  two  similar  pieces  in  a  saturated 
solution  of  oxalic  acid.  Without  rinsing,  immerse  one  piece  from 
each  acid  in  ammonia.  Dry  the  four  pieces  on  watch  glasses  in 
a  water  oven  at  60-80°  C.  (140  to  180°  F.).  Note  how  the  acids 
have  affected  the  strength  of  the  fabric.  Is  this  effect  produced 
by  the  cold  solutions  of  the  acids  ?  (Compare  the  pieces  in  which 
the  acid  was  neutralized  by  the  ammonia  before  drying.) 

It  is  sometimes  stated  that  the  injury  produced  by  organic 
acids,  such  as  oxalic  and  tartaric,  is  purely  mechanical,  due  to 
the  crystallizing  of  the  acids  in  the  fibers.  Do  your  results  sup- 
port this  view?  Can  you  suggest  other  methods  of  testing  this 
theory  ? 

When  acids  are  accidentally  spilled  upon  cotton  goods,  what 
means  should  be  taken  to  prevent  injury  to  the  fabrics  ? 

When  strong  alkalies  are  spilled  upon  cotton  goods,  how  are 
they  best  neutralized?  What  acids  may  be  used  and  what  pre- 
cautions should  be  observed  in  their  use  ? 

Explain  the  use  of  dilute  sulphuric  acid  in  the  purification  of 
wool  from  burrs  and  other  vegetable  matter.  (See  p.  221.) 

Cellulose  proper  —  e.g.  that  of  boiled-off  cotton  and 
bleached  linen  —  dissolves  readily  in  the  cold  in  concen- 


232  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

trated  sulphuric  acid  and  in  strong  solutions  of  certain  salts 
in  concentrated  hydrochloric  acid.  Among  such  salts  are 
mercuric  chloride  and  zinc  chloride.  A  hot  concentrated 
solution  of  the  latter  salt  (being  much  hydrolyzed)  will  dis- 
solve cellulose  without  the  addition  of  any  hydrochloric  acid. 
Before  going  into  solution  in  any  of  these  reagents  the 
fibers  swell  and  soften,  probably  on  account  of  the  combining 
of  water  with  the  cellulose.  This  swelling  is  utilized  in  the 
manufacture  of  parchment  paper  and  in  one  of  the  processes 
of  waterproofing  cotton  goods. 

Experiment  139. 

Pour  20  cc.  concentrated  sulphuric  acid  into  10  cc.  water  in  a 
beaker  or  dish.  Allow  to  cool  to  room  temperature.  Provide  another 
beaker  or  dish  of  water.  Dip  a  strip  of  filter  paper  into  the  acid 
for  about  five  seconds,  then  transfer  it  quickly  to  the  water.  Wash 
thoroughly.  Compare  the  appearance  and  strength  of  the  treated 
paper  with  that  of  wet  untreated  filter  paper.  Treat  each  with 
iodine  solution. 

Cellulose,  being  carbohydrate,  has  the  characteristics  of 
an  alcohol  (with  many  — OH  groups).  It  is,  therefore,  ca- 
pable of  reacting  with  acids  to  form  esters  and,  having  many 
— OH  groups,  it  can  form  several  esters  with  one  acid.  The 
nitrates  of  cellulose  are  made  commercially,  not  only  for  use 
as  explosives,  but  also  for  the  manufacture  of  collodion  and 
artificial  silk.  Cellulose  is  nitrated  by  treatment  with  a 
mixture  of  nitric  acid  and  concentrated  sulphuric  acid. 
Cellulose  nitrates  are  commonly  called  nitrocelluloses. 

Experiment  140. 

Mix  20  cc.  concentrated  sulphuric  acid  and  10  cc.  concentrated 
nitric  acid.  Allow  to  cool  to  room  temperature.  Immerse  absorbent 
cotton  in  this  mixture  for  about  one  minute.  Wash  thoroughly  with 
cold  water,  wring  out,  and  allow  to  dry  on  filter  paper.  Set  a  piece 
of  the  dry  product  and  a  piece  of  the  untreated  cotton  on  fire  and 
compare  the  rapidity  with  which  they  burn. 


TEXTILE   FIBERS   OF  VEGETABLE  ORIGIN          233 

This  product  is  a  "nitrocellulose"  (guncotton  or  pyroxylin). 
Shake  a  portion  of  the  dry  guncotton  with  a  mixture  of  alcohol 
and  ether.  (A  residue  of  unchanged  cellulose  will  remain.) 
The  clear  liquid  (a  solution  of  nitrocellulose  in  ether  and  alcohol) 
is  collodion.  Pour  a  little  of  it  on  a  glass  plate  and  allow  to 
evaporate.  (Keep  flames  away.)  Surgeons  sometimes  use 
collodion  to  form  a  coating  over  wounds.  Such  a  coating  is 
adherent,  flexible,  and  impermeable  to  air  and  water. 

Experiment  141. 

Material : 

Collodion  prepared  in  the  preceding  experiment. 

Pour  a  little  of  the  collodion  solution  on  water  in  a  test  tube. 
Note  that  it  forms  a  clear  layer  above  the  water.  Shake  the  tube. 
The  precipitate  is  nitrocellulose. 

Experiment  142.  —  Action  of  Alkalies. 

Boil  a  piece  of  cotton  yarn  or  woven  cotton  goods  for  a  few 
minutes  with  dilute  sodium  hydroxide  solution.  Wash,  neu- 
tralize the  alkali  by  dipping  into  water  containing  a  little  acetic 
acid,  and  wash  again.  Compare  the  strength  of  the  goods  with 
that  of  untreated  cotton  of  the  same  kind.  Contrast  the  effect 
of  alkalies  on  cotton  with  that  on  wool  and  silk.  How  could  this 
difference  be  utilized  in  the  analysis  of  mixed  goods? 

Experiment  143.  —  Action  of  Alkalies. 

Cover  a  piece  of  cotton  with  a  strong  solution  of  caustic  soda 
(30  per  cent)  or  caustic  potash  (50  per  cent)  and  allow  to  stand 
10  or  15  minutes.  Remove  the  cotton,  wash  in  a  stream  of  cold 
water,  dip  into  dilute  acetic  acid,  and  wash  again.  Note  the  ap- 
pearance of  the  cotton,  comparing  it  with  that  of  untreated  cotton. 


Mercerization 

Mercerization  is  a  process  to  which  cotton  is  sometimes 
subjected  to  increase  its  luster,  its  strength  and  wearing 
qualities,  and  its  capacity  for  taking  dyes.  The  cotton  is 
stretched  on  a  frame  and  subjected  to  the  action  of  a  strong 
cold  solution  of  sodium  hydroxide  (about  30  per  cent  NaOH), 
after  which  it  is  washed  with  water.  The  effect  of  the  strong 


234  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

solution  of  alkali  on  unstretched  cotton  is  to  swell  and  shorten 
the  fiber,  causing  shrinkage  of  the  goods.  When  the  goods 
are  stretched,  the  shrinkage  is  overcome  or  prevented,  but 
the  fibers  are  untwisted  and  acquire  a  high  luster.  It  is 
supposed  that  the  alkali  hydroxide  combines  chemically 
with  the  cellulose,  and  that,  on  washing,  the  metal  of  the 
alkali  is  replaced  by  hydrogen,  leaving  hydrated  cellulose,  i.e. 
a  compound  of  cellulose  with  water. 

The  process  takes  its  name  from  John  Mercer,  who  in  1844 
first  observed  the  action  of  concentrated  solutions  of  the  caustic 
alkalies  on  cotton,  and  in  1850  took  out  a  patent  on  the  process. 
The  stretching  of  the  fabric  to  prevent  shrinkage  and  produce  a 
high  luster  was  a  later  development  introduced  by  Lowe  in  1889. 
It  is  only  since  this  later  discovery  that  the  process  has  become 
commercially  successful.  Long-stapled  cottons  (Egyptian  and 
Sea  Island),  which  are  naturally  more  glossy  than  the  commoner 
short-stapled  varieties,  are  preferred  in  the  manufacture  of  mer- 
cerized goods. 

Sizing,  or  Dressing  of  Cotton  Goods 

Cotton  goods  are  commonly  sized  or  otherwise  finished 
to  give  an  attractive  (sometimes  a  deceptively  attractive) 
appearance.  In  the  trade,  the  term  sizing  is  commonly 
used  to  designate  the  process  of  applying  dressing  materials 
to  the  warps,  while  the  application  of  the  same  materials 
to  the  woven  fabric  is  termed  finishing.  Among  the  mate- 
rials used  for  various  purposes  are : 

(a)  Stiffening  agents :   starch,  flour,  dextrin,  glue,  gelatin,  gums. 

(b)  Softening  agents :  fats,  waxes,  soaps. 

(c)  Filling  and  weighting  agents :    aluminium  silicate   (China 
clay),  calcium  sulphate  (gypsum),  magnesium  silicate  (talc),  calcium 
carbonate  (whiting),  barium  sulphate  (blanc  fixe). 

(d)  Hygroscopic  agents  —  which  both  add  weight  and  soften : 
magnesium  chloride,  calcium  chloride,  glycerin. 

(e)  Preservative  agents  —  to  prevent  the  growth  of  mildew  and 
other  organisms :  zinc  chloride,  carbolic  acid,  cresols,  salicylic  acid, 
boric  acid. 


TEXTILE   FIBERS   OF   VEGETABLE  ORIGIN         235 

The  basis  of  the  size  is  practically  always  starch.  This 
can  be  removed  by  boiling  with  dilute  acid,  which  hydrolyzes 
it  and  thus  loosens  the  filling  materials.  Subsequent  treat- 
ment with  dilute  alkali  removes  the  fats  and  waxes. 

Experiment  144. — Determination  of  Dressing  Materials. 

Material : 

White  cotton  goods,  unwashed. 

•  Wet  a  small  portion-  of  the  goods  and  test  with  iodine  solution 
for  starch.  Prepare  a  3  per  cent  solution  of  hydrochloric  acid 
(by  diluting  400  cc.  of  the  reagent  dilute  hydrochloric  acid  to 
i  liter)  and  a  i  per  cent  solution  of  sodium  carbonate  (by  diluting 
100  cc.  of  the  reagent  solution  to  i  liter). 

Weigh  a  piece  of  the  dry  goods  (2  to  5  grams).  Boil  10  or  15 
minutes  in  the  3  per  cent  hydrochloric  acid.  Cool,  rinse,  and  test 
for  starch.  If  present,  boil  again  with  the  acid.  Rinse  and  boil  5 
minutes  in  i  per  cent  sodium  carbonate  solution.  Rinse  thoroughly, 
dry,  allow  to  stand  in  the  air  of  the  room  for  2  or  3  hours,  and  weigh. 
The  difference  between  the  initial  and  the  final  weight  is  the  weight 
of  the  dressing  materials. 


Linen 

Linen  is  a  bast  (i.e.  inner  bark)  fiber  obtained  from  flax 
stalks.  These  are  cut  or  pulled,  while  still  somewhat  green, 
stripped  of  seeds  and  leaves  by  a  machine,  and  then  subjected 
to  a  fermentation  known  as  "  retting  "  —  i.e.  rotting.  Ret- 
ting is  conducted  either  in  water  (tanks  or  running  streams) 
or  by  exposure  to  the  weather  (dew  retting)  or  both.  Its 
effect  is  to  convert  the  substances  holding  the  fibers  together 
into  soluble  compounds  which  are  washed  out.  Thus  an 
enzyme  (pectinase)  secreted  by  certain  bacteria  acts  upon 
the  calcium  pectate  between  the  cells,  converting  it  into 
pectin,  sugars  and  soluble  calcium  salts.  The  remaining 
impurities  —  bark,  woody  tissue,  etc.  —  are  removed  by  me- 
chanical processes,  and  the  fiber  then  undergoes  much  the 
same  treatment  as  cotton. 


236  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Experiment  145. 

Examine  unbleached  and  bleached  linen  fibers  under  the  mi- 
croscope, comparing  them  with  cotton  fibers.  Moisten  with  a 
dilute  solution  of  iodine  and  examine  again. 

Note  particularly  the  absence  of  twist  and  the  presence  of  cross- 
markings  at  the  junctions  of  the  cells  —  similar  to  the  "  knots  " 
in  straw. 

Linen  fibers  are  from  8  inches  to  5  feet  long,  averaging  20 
inches,  and  from  -jTnnr  to  TFIT  mcri  m  diameter,  averaging 
about  -nnnr  inch.  They  are  thus  much  longer,  and  on  the 
average  a  little  coarser  than  cotton  fibers.  Under  the  mi- 
croscope the  flax  fiber  appears  as  a  long,  straight,  cylindrical 
tube  with  a  narrow  lumen,  often  appearing  as  a  mere  black 
streak.  There  are  cross  markings  on  the  cylinder,  and  nodes 
resembling  the  knots  on  straw.  These  markings,  which 
are  emphasized  by  treatment  with  iodine,  constitute  one  of 
the  best  means  of  identifying  linen  fibers.  The  natural  ends 
of  the  flax  fibers  are  narrow  and  pointed. 

The  flax  fiber  is  not,  like  the  cotton  fiber,  a  single  cell,  but 
consists  of  a  bundle  of  cells,  averaging  about  i  inch  in  length 
and  Tnnr  inch  in  diameter  at  the  middle.  The  fiber  of  flax 
is  more  porous  than  that  of  cotton,  and  the  following  very 
good  test,  particularly  for  bleached  goods,  is  based  upon  this 
property. 

Experiment  146.  —  Oil  Test  for  Linen. 

Free  the  sample  from  dressing  by  boiling  in  3  per  cent  hydro- 
chloric (or  5  per  cent  oxalic)  acid.  Treat  with  i  per  cent  sodium 
carbonate  solution,  rinse  with  distilled  water,  and  dry.  Fringe 
out  the  goods  on  two  adjacent  edges,  so  as  to  expose  ends  of  warp 
and  weft  threads.  Moisten  the  piece  thoroughly  with  olive  oil 
or  glycerin.  Press  between  filter  papers  and  place  against  a  dark 
background.  The  linen  fibers  or  threads  appear  translucent, 
the  cotton  fibers  remain  opaque  white. 

The  linen  fiber  is  stronger,  but  harder  and  less  resilient 
(elastic)  than  cotton.  It  is  also  a  better  conductor  of  heat 


TEXTILE   FIBERS  OF   VEGETABLE   ORIGIN         237 

and  therefore  feels  cooler  to  the  touch.  Experts  can  some- 
times distinguish  cotton  goods  from  linen  by  feeling  them. 
Dressings,  however,  may  interfere  here. 

Bleached  linen,  like  bleached  cotton,  is  almost  pure  cellu- 
lose. Unbleached  flax  fiber,  however,  contains  from  0.5  to 

2  per  cent  of  a  wax-like  substance  and  2.5  to  10  per  cent  of 
intercellular  substance  and  pectins.     Unbleached  or  incom- 
pletely bleached  linen  often  shows  a  noticeable  difference 
from  cotton  on  treatment  with  staining  materials.     Many 
distinguishing  tests  have  been  based  upon  this  fact. 

Experiment  147. 

Materials : 

Rosolic  acid  solution  (0.5  gram  in  50  cc.  water  and  50  cc. 

alcohol). 

Samples  of  pure  cotton  and  pure  linen  goods. 
Sample  with  linen  warp  and  cotton  weft. 

Warm  the  mixture.  Fringe  out  the  samples  on  two  adjacent 
edges  and  immerse  in  the  solution  for  five  minutes.  Remove, 
wash  with  water,  with  dilute  ammonia,  and  again  with  water, 
Dip  into  concentrated  sodium  hydroxide  solution;  again  wash 
thoroughly,  and  allow  to  dry.  Note  which  of  the  materials  is 
permanently  reddened. 

Experiment  148. 

Materials : 

Cyanin  solution  (o.i    gram  in   50  cc.    alcohol  and    50  cc. 
water) . 

The  same  fabrics  as  in  Experiment  147. 
Fringe  out  the  samples,  warm  them  in  the  cyanin  solution  for 

3  minutes.     Wash.     Lay  in  water  acidulated  with  sulphuric  acid, 
then  treat  with  dilute  ammonia. 

One  of  the  most  useful  tests  for  distinguishing  cotton 
from,  and  detecting  cotton  in,  linen  goods  is  treatment  with 
cold  concentrated  sulphuric  acid.  This  test  is  most  success- 
ful with  coarse-woven  goods,  such  as  towelings,  but  by  vary- 
ing the  time  of  immersion  may  be  made  to  succeed  even  with 
a  handkerchief  weave. 


238  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Experiment  149. 

Free  the  material  completely  from  dressing  by  boiling  with 
3  per  cent  hydrochloric  or  5  per  cent  oxalic  acid,  treating  with 
i  per  cent  sodium  carbonate  solution  and  rinsing  with  distilled 
water.  Dry  the  goods.  Immerse  in  concentrated  sulphuric 
acid  from  i|  to  2  minutes,  according  to  the  texture  of  the  material. 
Remove,  wash  thoroughly  with  water,  then  with  dilute  ammonia. 
Cotton  fibers  are  destroyed,  linen  fibers  remain. 

Linen  warp  threads  in  goods  with  cotton  weft  can  be  retained 
in  position  in  this  test  by  tying  the  goods  to  microscope  slides  with 
strong  linen  thread. 

Although  linen  is  more  resistant  to  sulphuric  acid  than 
cotton,  it  is  less  resistant  to  boiling  alkaline  solutions  and  to 
bleaching  powder  and  other  oxidizing  agents. 

The  dressing  materials  applied  to  linen  goods  are  similar 
to  those  used  for  cottons.  The  amount  of  hygroscopic  mois- 
ture in  linen  is  about  the  same  as  that  in  cotton,  viz.  6  to  8 
per  cent. 

Lustracellulose  ("  Artificial  Silk  ") 

"  Artificial  silk  "  fibers  are  made  from  cellulose  (cotton  or 
wood  pulp)  by  dissolving  it  in  a  suitable  solvent,  forcing  the 
solution  through  minute  openings,  and  reconverting  it  into 
a  solid  form  as  it  issues  in  fine  streams.  The  threads  thus 
produced  resemble  silk  in  structure,  being  formed  by  a 
process  similar  to  that  used  by  the  silk  worm.  In  size  (both 
length  and  diameter)  and  in  luster  they  approximate  much 
more  closely  to  silk  fibers  than  do  mercerized  cotton  fibers. 
Chemically  they  are  not  protein,  like  the  fibroin  of  silk,  but 
carbohydrate,  viz.  cellulose.  From  the  chemical  standpoint, 
therefore,  the  name  lustracellulose  is  preferable  to  artificial 
silk. 

Attempts  have  been  made  to  manufacture  artificial  protein 
fibers  from  gelatin  and  from  casein.  These  processes,  however, 
have  not  been  commercially  successful. 


TEXTILE   FIBERS   OF  VEGETABLE  ORIGIN         239 

The  three  leading  processes  of  manufacturing  artificial 
silk  are: 

1 .  That  known  from  its  inventor  as  the  Chardonnet  Process 
and  from  its   intermediate  products   as   the  Pyroxylin  or 
Collodion  Process.     The   cellulose  is   converted  into  nitro- 
cellulose by  treatment  with  nitric  and  sulphuric  acids.    (See 
Expt.  140,  p.  232.)     The  nitrocellulose  is  dissolved  in  ether 
and  alcohol  and  the  resulting  collodion  forced  through  the 
narrow  openings  into  a  warm  chamber.     The  alcohol  and 
ether  evaporating  from  the  threads  are  recovered  and  used 
over  and  over  again.     The  nitrocellulose  fibers  are  recon- 
verted into  cellulose  ("  denitrated  ")  by  immersion  in  a  solu- 
tion of  ammonium  sulphide. 

The  Chardonnet  Process,  although  expensive,  is  still  in  use 
in  France. 

2.  The  Cuprate  or  Cuprammonium  Process.      The  cellu- 
lose is  dissolved  in  an  ammoniacal  solution  of  copper  hy- 
droxide and  the  threads  delivered  into  an  acid,  which  re- 
precipitates  the  cellulose.     This  process  is  used  principally  in 
Germany. 

3.  The  Viscose  Process.       The  cellulose   (usually  wood 
pulp)  is  treated  with  a  strong  caustic  soda  solution  such  as  is 
used  in  mercerizing.     The  alkali  cellulose  thus  obtained  is 
treated  with  carbon  disulphide.     Combination  occurs  with 
the  production  of  a  compound  soluble  in  water,  but  insoluble 
in  alcohol  and  in  brine.     This  compound  is  called  "  viscose  " 
on  account  of  the  extraordinary  viscosity  of  its  solution  in 
water.     The  viscous  solution  is  forced  through  fine  openings 
into  a  concentrated  solution  of  sodium  chloride  or  ammonium 
chloride   which   precipitates   the   viscose   in   threads.     The 
latter  is  then  decomposed  by  heat  into  cellulose  and  water- 
soluble  products,  which  latter  are  washed  out. 

The   chemical   reactions   involved   in   the    Pyroxylin    Process 
are  illustrated  by  Experiments  140  and  141  above. 


240  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Experiment  150. — The  Cuprate  Process. 

Dilute  10  cc.  copper  sulphate  solution  to  about  150  cc.  in 
a  beaker.  Add  a  few  drops  ammonium  chloride  solution,  and, 
without  heating,  add  sodium  hydroxide  solution  until  the  precipi- 
tate formed  just  begins  to  darken  in  color.  Allow  to  settle, 
filter,  and  wash  the  precipitate  with  cold  water.  (What  is  this 
precipitate  ?)  Remove  the  precipitate  from  the  filter  paper,  place 
it  in  a  dish,  cover  with  ammonium  hydroxide,  and  stir.  Pour  off 
the  clear  solution  into  a  test  tube,  add  some  absorbent  cotton,  and 
shake.  Pour  a  little  of  the  solution  thus  obtained  into  dilute  acid 
in  a  test  tube.  The  precipitate  is  the  regenerated  cellulose. 

Experiment  151.  — The  Viscose  Process. 

Cover  a  little  absorbent  cotton  in  a  beaker  with  30  per  cent 
sodium  hydroxide  (or  50  per  cent  potassium  hydroxide)  solution 
and  allow  to  stand  for  an  hour  or  longer.  Remove  the  alkali- 
cellulose  from  the  liquid  by  use  of  a  glass  rod.  (Better  results 
will  be  obtained  if  the  moist  mass  is  now  placed  in  a  stoppered 
bottle  or  test  tube  and  allowed  to  stand  two  or  three  days.  This, 
however,  is  not  essential  to  the  success  of  the  experiment.) 

Cover  the  moist  mass  with  carbon  disulphide,  shake  vigorously, 
and  allow  to  stand  until  quite  yellow  (about  3  hours).  Pour  off 
the  excess  of  carbon  disulphide,  cover  the  product  with  water, 
and  again  allow  to  stand  for  an  hour  or  more.  Shake,  and  add 
enough  additional  water  to  give  a  thick  brown  liquid.  This  is 
the  viscose  solution.  Pour  portions  of  it  into  (a)  alcohol,  (b)  a 
saturated  solution  of  ammonium  chloride.  A  portion  may  also 
be  forced  through  a  piece  of  glass  tubing  drawn  to  a  capillary. 
Dip  the  capillary  end  of  the  tube  under  the  surface  of  alcohol  or 
saturated  ammonium  chloride  solution  and  blow  steadily  into  the 
tube.  The  viscose  will  precipitate  in  threads. 

Pour  the  main  portion  of  viscose  solution  into  a  small,  flat-bot- 
tomed dish  (a  crystallizing  dish),  cover  it  with  alcohol,  and  allow 
to  stand  half  an  hour.  Pour  off  the  alcohol,  being  careful  not  to 
disturb  the  sediment  of  viscose.  Rinse  two  or  three  times  with 
alcohol,  then  heat  on  a  water  bath.  The  viscose  is  decomposed 
by  the  heat.  Rinse  the  dry  residue  several  times  with  water. 
This  removes  the  other  decomposition  products,  leaving  the  cel- 
lulose in  the  form  of  a  film. 


TEXTILE   FIBERS  OF  VEGETABLE  ORIGIN         24! 

Experiment  152. 

Materials : 
Artificial  silk. 
True  silk. 
Mercerized  cotton. 

Ravel  out  threads  of  each.  Could  the  mercerized  cotton  be 
recognized  by  the  length  of  the  fibers  ? 

Break  equal-sized  threads  of  each,  comparing  the  strength  of 
the  threads. 

Wet  each  thoroughly  and  again  compare  the  strength  of  the 
threads. 

Burn  a  little  of  each  and  note  odor. 
How  can  you  distinguish  : 

(a)  Artificial  silk  from  mercerized  cotton. 

(b)  Lustracellulose  from  silk. 

The  following  methods  may  be  used  for  the  quantitative 
analysis  of  mixtures  of  cotton  and  wool  and  of  cotton  and 
silk. 

Experiment  153.  —  Analysis  of  a  Wool-cotton  Fabric. 

Materials : 

Fabric  containing  wool  and  cotton. 

5  per  cent  solution  of  potassium  hydroxide. 

i  per  cent  solution  of  hydrochloric  acid. 

0.05  per  cent  solution  of  sodium  carbonate. 
Weigh  the  sample.  Remove  the  finishing  materials  by  boiling 
30  minutes  in  i  per  cent  hydrochloric  acid,  rinsing,  and  boiling 
thirty  minutes  in  0.05  per  cent  sodium  carbonate.  Wash  thoroughly, 
air-dry,  and  weigh.  The  loss  represents  finishing  materials. 
Dry  to  constant  weight  in  a  water  oven.  The  loss  represents 
moisture,  and  the  residue  is  dry  fiber. 

Boil  for  20  minutes  in  5  per  cent  caustic  potash.  Wash  well, 
dry  in  the  water  oven  to  constant  weight.  Add  5  per  cent  to 
the  weight  of  the  residue,  because  the  cotton  is  attacked  to  about 
that  extent.  The  residue  is  the  weight  of  dry  cotton,  the  loss  that 
of  dry  wool. 

Experiment  154.  — Analysis  of  a  Silk-cotton  Fabric. 

Materials : 

Fabric  of  silk  and  cotton. 

Eisner's  reagent  (basic  zinc  chloride). 


242  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Determine  the  quantities  of  finishing  material  and  moisture  as  in 
Experiment  153. 

Immerse  in  the  boiling  basic  zinc  chloride  solution  for  one 
minute.  Wash  thoroughly  with  i  per  cent  hydrochloric  acid, 
then  with  water ;  dry  and  weigh.  Add  i|  per  cent  to  the  weight 
of  the  residue.  The  result  represents  the  amount  of  cotton. 

The  silk  may  also  be  dissolved  by  immersion  for  5  minutes  at 
room  temperature  in  Richardson's  reagent  (an  ammoniacal  solu- 
tion of  nickel  hydroxide)  or  for  15  minutes  at  50°  C.  in  Lowe's 
reagent  (an  alkaline  solution  of  copper  hydroxide  and  glycerol). 

Richardson's  reagent  is  prepared  by  dissolving  25  grams  nickel 
sulphate  in  500  cc.  water,  precipitating  completely  with  sodium 
hydroxide,  washing  thoroughly  by  settling  and  decantation, 
dissolving  in  125  cc.  concentrated  ammonia  and  making  up  to 
250  cc. 

Lowe's  reagent  is  prepared  by  dissolving  25  grams  copper 
sulphate  in  250  cc.  water,  adding  12  cc.  glycerol  and  just  sufficient 
sodium  hydroxide  solution  to  redissolve  the  precipitate  which 
forms  at  first. 

The  methods  of  manufacturing  cotton  and  linen  fabrics  and  their  properties 
in  relation  to  selection  and  use  are  fully  discussed  by  Woolman  and  McGowan  in 
the  work  already  referred  to  (p.  228). 


CHAPTER  XLII 

BLEACHING  AND   BLUEING 

WHILE  a  great  many  chemical  compounds  are  white  —  e.g. 
sugar,  salt,  starch  —  there  are  many  others  that  are  char- 
acterized by  certain  colors.  When  such  compounds  undergo 
chemical  change,  their  characteristic  colors  disappear  and 
the  colors  of  the  products  of  the  chemical  change  make  their 
appearance.  Indeed,  a  change  of  color  is  commonly  accepted 
as  an  indication  of  chemical  change. 

A  change  of  color  is  only  an  indication,  not  a  proof,  that  chem- 
ical change  has  taken  place.  The  color  of  a  solid  substance  may 
be  materially  altered  by  a  change  of  physical  condition.  Thus 
large  copper  sulphate  crystals  appear  dark  blue,  while  small 
crystals  are  lighter  blue ;  cold  zinc  oxide  is  white,  but  hot  zinc 
oxide  yellow. 

To  bleach  a  textile,  whether  for  the  purpose  of  removing  the 
natural  color  of  the  fiber  or  to  take  out  a  stain  or  to  remove 
a  dye,  what  must  be  done  is  to  convert  the  color-bearing  com- 
pound or  compounds  into  colorless  products.  The  natural 
coloring  matters  of  textile  fibers,  and  practically  all  the  dyes 
which  are  used  upon  textiles,  are  organic  substances,  i.e.  car- 
bon compounds.  There  are  two  general  methods  of  convert- 
ing organic  coloring  matters  into  colorless  products : 

i.  By  Oxidation. — This  may  be  accomplished  by  the 
action  of  free  oxygen,  especially  under  the  influence  of  direct 
sunlight.  The  "  grass  bleaching  "  of  linen  is  a  familiar  ex- 
ample. More  rapid  action  can,  as  a  rule,  be  attained  by  the 
use  of  an  oxidizing  agent,  i.e.  a  compound  which  readily  gives 
up  oxygen  to  other  substances.  Among  the  oxidizing  agents 
used  in  bleaching  are  calcium  hypochlorite,  sodium  hypo- 
chlorite,  hydrogen  peroxide,  and  potassium  permanganate. 

243 


244  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

2.  By  Action  of  Sulphurous  Acid,  H2SO3.  —  Sulphurous 
acid  is  a  reducing  agent  (see  Expt.  98,  p.  169),  being  readily 
oxidized  to  sulphuric  acid,  H2SO4.  No  doubt  in  many  in- 
stances it  bleaches  by  removing  oxygen  from  the  color- 
bearing  compound.  But  it  also  has  the  power  of  combining 
with  some  kinds  of  organic  substances,  and  its  bleaching  action 
may  often  be  due  to  combination  rather  than  to  reduction. 
Its  action  is  in  many  instances  not  fully  understood. 

In  the  removal  of  the  natural  colors  from  textile  fabrics 
the  choice  of  a  bleaching  agent  must  be  governed  by  its  effect 
upon  the  fiber  substance  itself,  as  well  as  by  its  cost  and  its 
effectiveness  in  destroying  the  coloring  matter.  In  house- 
hold bleaching,  likewise,  the  effect  of  the  bleaching  agent 
upon  the  material  to  be  bleached  must  be  known  and  borne 
in  mind. 

Hypochlorites 

The  most  active  bleaching  agent,  and  the  cheapest  except 
atmospheric  oxygen,  is  bleaching  powder. 

This  is  made  by  the  combining  of  chlorine  with  lime, 
whence  the  alternative  name,  chloride  of  lime.  It  has  the 
composition  represented  by  the  formula  CaOC^,  and  when 
dissolved  in  water  ionizes  thus : 

CaOCl2  =  Ca++  +  Cl~  +  OCr 

The  hypochlorite  ions,  OC1~,  readily  give  up  oxygen, 
especially  in  presence  of  acid,  where  they  first  unite  with 
hydrogen  ions,  H+,  to  give  the  unstable  hypochlorous  acid, 
HC1O.  Bleaching-powder  solutions,  therefore,  especially 
when  acidified,  act  as  strong  oxidizing  agents. 

Experiment  155.  —  Bleaching  Powder. 

Materials : 

Bleaching  powder. 
Mortar  and  pestle. 
Cobalt  nitrate  solution  (10  per  cent). 


BLEACHING  AND   BLUEING  245 

Grind  about  10  grams  bleaching  powder  in  a  mortar,  and  gradually 
add  about  5  grams  of  water  so  as  to  form  a  paste.  Add  an  addi- 
tional 25  cc.  water,  mix  thoroughly,  and  filter.  Note  the  odor 
of  the  filtrate.  Heat  a  portion  of  it  and  note  whether  the  odor 
becomes  stronger.  Also  note  whether  a  precipitate  forms.  The 
odor  is  that  of  hypochlorous  acid  and  the  precipitate  is  calcium 
hydroxide.  What  effect  do  you  infer  that  heat  has  on  the  hydrol- 
ysis of  calcium  hypochlorite  ? 

To  a  portion  of  the  nitrate  add  a  few  drops  of  cobalt  nitrate 
solution,  cover  the  test  tube  with  the  thumb  for  a  minute  or  so, 
then  test  the  evolving  gas  with  a  glowing  splint.  What  is  the  gas  ? 
Is  it  pure?  (Note  odor.)  The  black  precipitate,  which  is  an 
oxide  of  cobalt,  acts  as  a  catalytic  agent,  causing  rapid  decomposi- 
tion of  the  hypochlorous  acid. 

To  a  portion  of  the  original  filtrate  add  dilute  hydrochloric  acid. 
Note  color  and  odor.  These  are  due  to  chlorine,  hydrochloric 
and  hypochlorous  acids  reacting  thus : 

HC1  +  HC1O  =  H2O  +  C12 

Experiment  156.  —  Bleaching  Effect. 

Materials  : 

Bleaching-powder  solution  prepared  as  in  Experiment  155. 
Small  pieces  of  cotton  fabric  dyed   or   printed  in  various 

colors. 

Immerse  the  pieces  of  cotton  in  the  bleaching-powder  solution 
for  a  few  minutes.  Then  dip  in  dilute  hydrochloric  acid.  Repeat 
the  treatment  with  bleaching  powder  and  dilute  hydrochloric 
acid  several  times,  noting  the  effect  on  the  colors. 

Experiment  157.  —  Effect  on  Textile  Materials. 

Materials : 

Bleaching-powder    solution    prepared     as    in    Experiment 

155- 

Sodium   bisulphite   solution  or  sodium    thiosulphate    solu- 
tion. 
White  or  unbleached  cotton,  linen,  silk,  and  wool,  in  yarns  or 

light  fabrics. 

Immerse  the  textiles  in  the  bleaching-powder  solution  for  a 
few  minutes,  then  dip  in  dilute  hydrochloric  acid,  and  finally  in 
sodium  bisulphite  solution.  Rinse  and  dry.  Note  how  the  color 
and  strength  of  the  materials  have  been  affected. 


246  ELEMENTARY  HOUSEHOLD    CHEMISTRY 

Experiment  158.  —  Formation  of  Oxycellulose. 

Materials : 

White  cotton  or  linen  goods. 
Bleaching-powder  solution. 
Sodium  bisulphite  solution. 

Immerse  three  equal-sized  pieces  of  the  goods  in  the  bleaching- 
powder  solution  for  about  five  minutes.  Dry  one  without  rinsing. 
Treat  the  second  with  dilute  hydrochloric  acid  and  the  third  with 
sodium  bisulphite  (or  with  sodium  thiosulphate)  solution;  rinse 
.and  dry. 

When  the  three  pieces  are  dry,  compare  their  strengths  and 
colors. 

Experiment  159.  —  Detection  of  Oxycellulose. 

Thoroughly  wash  the  piece  of  cotton  dried  with  the  bleaching 
powder  in  it  (Expt.  158).-  Cover  it  with  Fehling-Benedict  solution 
and  boil.  For  comparison  boil  a  piece  of  untreated  cotton  with 
Fehling-Benedict  solution.  Oxycellulose  reduces  the  solution, 
the  precipitate  of  cuprous  hydroxide  being  deposited  upon  the 
fiber. 

Industrially,  silk  is  never  treated  with  bleaching  powder 
or  other  hypochlorites.  In  the  woolen  industry  bleaching 
powder  is  not  used  for  bleaching  purposes,  though  it  is 
sometimes  used  to  render  woolen  goods  unshrinkable  —  not, 
however,  without  injury  to  the  wearing  qualities.  In  the 
commercial  bleaching  of  cotton  and  linen,  however,  it  is 
universally  used.  Great  care  has  to  be  exercised  to  prevent 
the  formation  of  Oxycellulose,  which  both  tenders  the  goods 
and  makes  them  dye  unevenly.  Special  care  is  necessary  in 
the  case  of  linen,  which  has  more  natural  color  to  remove 
and  at  the  same  time  has  a  more  easily  injured  fiber  than 
cotton.  Weaker  solutions  are  used  for  linen,  the  treatments 
being  more  numerous  and  the  bleaching-powder  treatment 
("  chemicking ")  being  alternated  with  treatments  with 
alkalies  and  supplemented  by  grass  bleaching. 

Cotton  bleaching  is  accomplished  by  alternate  treatments 
with  bleaching-powder  solution  ("  chemicking  ")  and  with 


BLEACHING  AND   BLUEING  247 

dilute  hydrochloric  acid  ("  souring  ")•  The  acid  acts  on  the 
bleaching  powder  left  in  the  material,  converting  it  into 
chlorine  and  calcium  chloride,  which  are  readily  washed  out. 
If  solid  particles  of  bleaching  powder  are  allowed  to  come 
into  contact  with  the  goods,  or  if  the  goods  are  exposed  to 
air  and  right  before  the  hypochlorite  has  been  completely 
removed,  oxy  cellulose  is  apt  to  be  formed.  Much  damage 
is  no  doubt  done  in  domestic  and  commercial  laundries 
through  the  ignorant  use  of  bleaching  powder.  Washing 
with  water  ought  not  to  be  depended  upon  to  remove  the 
reagent  from  the  goods.  Effective  materials  for  this  purpose, 
less  disagreeable  in  their  effects  than  the  hydrochloric  acid 
(which  is  preferred  in  factory  practice  for  economical  reasons), 
are  sodium  bisulphite,  NaHSO3,  and  sodium  thiosulphate, 
,  commonly  known  as  hyposulphite  of  soda. 


Experiment  160. 

Materials  : 

Bleaching-powder  solution. 
Pieces  of  dyed  or  printed  cotton. 

To  a  filtered  solution  of  bleaching  powder  add  sodium  carbonate 
solution  as  long  as  a  precipitate  is  formed.  The  precipitate  is 
calcium  carbonate.  Write  equation  for  the  reaction.  What  com- 
pounds are  left  in  solution?  Filter. 

Immerse  pieces  of  colored  cotton  in  the  liquid,  afterwards  treat- 
ing with  dilute  hydrochloric  acid. 

The  solution  obtained  by  the  interaction  of  sodium  car- 
bonate and  chloride  of  lime  contains  sodium  chloride  and 
sodium  hypochlorite.  The  latter  has  a  bleaching  action 
similar  to  that  of  the  calcium  compound  and  has  the  ad- 
vantage of  avoiding  the  impregnation  of  the  goods  with  cal- 
cium salts  which  may  afterwards  react  with  soaps,  producing 
deposits  of  the  insoluble  lime  soaps.  It  finds  use  in  the  house- 
hold for  the  removal  of  stains  from  fabrics  by  bleaching. 

Sodium  hypochlorite  can  also  be  prepared  by  passing  chlorine 
gas  into  a  dilute,  cold  solution  of  sodium  hydroxide  or  sodium 


248  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

carbonate  and  by  passing  an  electric  current  through  a  solution 
of  common  salt.  In  either  case  the  solution  obtained  contains 
sodium  chloride  as  well  as  sodium  hypochlorite. 

This  solution  is  popularly  known  as  Javel  water  (commonly 
misspelled  Javelle  or  Javelles)  although  that  name  belonged 
originally  to  the  corresponding  potassium  product,  which  was  first 
made  in  the  Javel  bleach  works  near  Paris  in  1792.  In  pharmacy 
the  sodium  solution  is  known  as  Labarraque's  solution. 
•  •* 

Hydrogen  Peroxide 

Hydrogen  peroxide  is  a  compound  of  hydrogen  and  oxygen 
containing  a  higher  percentage  of  oxygen  than  does  water. 
Its  formula,  H2O2,  expresses  the  fact  that  the  proportion  of 
oxygen  to  hydrogen  is  twice  as  great  as  in  water,  H2O;  in 
other  words,  that  its  molecule  contains  two  atoms  of  oxygen 
combined  with  two  atoms  of  hydrogen.  In  acting  as  an 
oxidizing  agent  hydrogen  peroxide  gives  up  half  its  oxygen 
(i.e.  one  atom  from  each  molecule),  and  water  remains. 

Pure  hydrogen  peroxide  is  a  liquid  resembling  water,  but 
heavier  and  more  viscous.  It  is  an  unstable  substance,  de- 
composing spontaneously  into  water  and  oxygen.  For  this 
reason  it  is  not  easy  to  make  or  to  keep,  and  the  common 
commercial  hydrogen  peroxide  is  only  a  3  per  cent  aqueous 
solution. 

As  a  bleaching  agent  hydrogen  peroxide  has  the  advantages 
over  all  others,  except  oxygen  and  ozone,  that  it  does  not 
injure  the  most  sensitive  of  the  textile  fibers  and  that  it 
leaves  no  solid  residue  in  the  goods.  It  is  used  in  a  mildly 
alkaline  medium,  being  less  stable  in  alkaline  than  in  acid 
solutions  and  therefore  more  rapid  in  its  action.  It  is  em- 
ployed in  the  bleaching  of  feathers  and  ivory. 

Experiment  161. 

Materials  : 

Hydrogen  peroxide  solution. 
Manganese  dioxide,  powdered. 
Feather. 


BLEACHING  AND   BLUEING  249 

Colored  hair. 
Ecru  silk. 

To  5  cc.  hydrogen  peroxide  in  a  test  tube  add  a  little  powdered 
manganese  dioxide.  Test  the  evolved  gas  with  a  glowing  splint. 
What  is  the  gas? 

To  10  cc.  hydrogen  peroxide  in  a  beaker  add  ammonium  hy- 
droxide little  by  little  until  small  bubbles  begin  to  form.  Immerse 
the  feather,  hair,  and  ecru  silk,  and  examine  from  time  to  time. 

The  great  disadvantage  of  hydrogen  peroxide  as  a  bleach- 
ing agent  is  its  high  price.  This  can  to  some  extent  be 
obviated  by  preparing  the  hydrogen  peroxide  in  the  bleach- 
ing bath  itself  from  cheaper  materials.  Sodium  peroxide, 
Na2O2,  is  one  of  the  materials  from  which  it  is  obtained. 
Sodium  peroxide  reacts  with  acids,  liberating  hydrogen  per- 
oxide, thus : 

Na2O2  +  H2SO4  =  Na2SO4  +  H2O2 

In  use  the  sodium  peroxide  is  gradually  added  to  cold 
water.  The  solution  thus  obtained  is  neutralized  with  dilute 
sulphuric  acid  and  then  rendered  mildly  alkaline  by  the 
addition  of  sodium  silicate. 

Sodium  perborate,  NaBO3 .  4  H2O,  is  also  used  as  a  bleaching 
agent,  its  solution  behaving  like  one  of  borax  and  hydrogen 
peroxide. 

Potassium  permanganate,  KMnC>4,  is  occasionally  used  as  a 
bleaching  agent.  In  acting  as  an  oxidizing  agent  it  yields  a  brown 
solid  residue.  This  residue  is  removed  by  treatment  with  sodium 
bisulphite. 

The  nature  of  sunlight  bleaching  is  obscure.  It  is  possible  that 
the  action  of  the  sunlight  on  the  evaporating  water  produces 
hydrogen  peroxide  or  ozone  (an  active  form  of  oxygen),  and  that 
this  product  acts  upon  the  coloring  matters. 

Sulphurous  Acid 
Experiment  162. 

Materials : 
Sulphur. 

Red  flower  or  fresh  grass. 
Pieces  of  colored  cotton, 


250  ELEMENTARY  HOUSEHOLD   CHEMISTRY 

Apparatus : 
Deflagrating  spoon. 
Glass  cylinder  or  beaker. 
Glass  plate. 

Ignite  a  small  quantity  (|  gram)  sulphur  in  a  deflagrating  spoon, 
lower  the  spoon  into  the  beaker  and  cover  with  the  glass  plate. 
Note  odor  of  gas  evolved.  This  gas  is  sulphur  dioxide,  S02.  Sus- 
pend in  the  beaker  a  red  flower  (e.g.  rose  or  carnation)  or  some 
grass  and  some  pieces  of  colored  cotton. 

Experiment  163. 

Materials : 

Sodium  bisulphite. 
Potassium  permanganate  solution. 
Apparatus  : 

Test  tube  with  one-holed  rubber  stopper  or  cork,  through 
which  passes  a  delivery  tube  bent  twice  at  right  angles  so 
as  to  reach  the  bottom  of  a  second  test  tube. 
Place  in  the  generator  test  tube  1-2  grams  sodium  bisulphite, 
cover  with  water,  and  add  a  few  cubic  centimeters  of  dilute  sul- 
phuric acid.  Fill  the  other  test  tube  with  water  and  pass  the  gas 
from  the  generator  into  the  water.  Note  the  odor  of  the  gas  and 
compare  it  with  that  obtained  by  burning  sulphur  (Expt.  162). 
What  is  the  gas?  Write  equation  for  its  formation.  Does  it 
appear  to  be  absorbed  by  the  water?  (Compare  size  of  bubbles 
as  they  leave  the  tube  with  those  which  escape  from  the  water.) 
Test  the  water  with  blue  litmus  paper.  What  do  you  infer  as  to 
the  character  of  the  substance  formed  by  the  combining  of  the 
gas  with  water?  Write  equation  for  this  reaction.  The  solution 
contains  sulphurous  acid.  Try  the  action  of  this  solution  on  the 
same  materials  as  were  exposed  to  the  action  of  the  gas  in  Experi- 
ment 162.  Add  a  little  of  the  solution  to  a  dilute  solution  of 
potassium  permanganate. 

Experiment  164. 

Materials : 

Sodium  bisulphite. 

Indigo  carmine  solution,  prepared  by  dissolving  indigo  carmine 
in  water  or  by  warming  i  gram  indigo  with  8  cc.  fuming 
sulphuric  acid  for  one  to  two  hours,  rinsing  into  a  flask  and 
making  up  to  i  liter. 


BLEACHING   AND   BLUEING  251 

To  indigo  carmine  solution  add  sodium  bisulphite  solution 
sufficient  to  discharge  the  blue  color.  To  one  portion  of  the  prod- 
uct add  dilute  sulphuric  acid,  to  a  second  ammonium  hydroxide. 

Sulphurous  acid,  H^SOs,  is  known  only  in  solution.  Its 
anhydride  is  the  gas  sulphur  dioxide,  SO2-  Being  dibasic, 
sulphurous  acid  forms  acid  salts,  e.g.  sodium  bisulphite, 
NaHSO3,  as  well  as  the  normal  salts,  such  as  sodium  sulphite, 
Na2SOs.  The  anhydride,  the  acid,  and  the  acid  sodium  salt 
are  all  used  as  bleaching  agents  in  the  textile  industries. 
The  gaseous  anhydride,  sulphur  dioxide,  finds  the  widest 
use.  The  usual  method  of  bleaching  wool  and  silk  is  to  burn 
sulphur  in  iron  or  brick  pans  in  a  chamber  in  which  the 
goods  are  suspended.  The  process  is  known  technically  as 
"  stoving."  As  a  little  sulphuric  acid  is  formed  in  the  burn- 
ing of  sulphur,  thorough  washing  should  follow  stoving. 

For  bleaching  on  a  small  scale  sodium  bisulphite  is  con- 
venient. The  goods  may  either  be  steeped  for  some  hours 
in  a  fairly  strong  (about  1 5  per  cent)  solution  of  the  bisulphite, 
then  passed  through  very  dilute  hydrochloric  acid,  and  finally 
washed  with  water ;  or  a  weak  solution  of  the  bisulphite 
may  be  acidified  with  hydrochloric  acid  and  the  goods 
soaked  several  hours  in  the  mixture,  which,  of  course,  con- 
tains free  sulphurous  acid. 

Wool  bleached  with  sulphurous  acid  or  bisulphite  is  readily 
affected  by  alkalies,  the  natural  yellow  color  returning  on 
washing  with  soap  or  soda. 

A  more  permanent  bleach  is  obtained  by  the  use  of  hydro- 
gen peroxide.  Black  or  brown  wools  and  hair  cannot  be 
bleached  white,  but  assume  a  golden  color  when  treated  with 
peroxide. 

Blueing 

In  addition  to  bleaching,  i.e.  chemical  alteration  of  the 
coloring  matters,  there  is  another  device  used,  both  indus- 
trially and  in  the  household,  to  give  yellowish  goods  a  pure 


ELEMENTARY  HOUSEHOLD   CHEMISTRY 

white  appearance.  Blue  and  yellow,  being  complementary 
colors,  neutralize  each  other  in  their  optical  effect.  Yellow- 
ish goods  can  therefore  be  made  white  by  treatment  with  a 
suitable  quantity  of  blue  coloring  matter.  The  materials 
used  for  this  purpose  are : 

1.  Ultramarine,   a   complex   compound   of   the   elements 
sodium,  aluminium,  silicon,  sulphur,  and  oxygen.     Originally 
found  as  a  rather  rare  mineral,  lapis  lazuli,  ultramarine  is 
now  made  synthetically  from   sodium   sulphate,  clay,  and 
sulphur  by  heating  with  a  carbonaceous  reducing  agent, 
such  as  charcoal  or  tar.     Ultramarine  is  insoluble  in  water, 
but  in  a  finely  divided  condition  remains  suspended  long 
enough  to  be  evenly  distributed  over  the  goods.     It  is  not 
affected  by  air,  light,  or  alkalies,  but  is  decomposed  by  dilute 
acids. 

2.  Indigo,  a  dye  formerly,  and  to  some  extent  still,  ob- 
tained by  the  fermentation  of  the  juices  of  certain  species  of 
plants  known  as  Indigofera,  but  now  manufactured  in  a 
purer  form  from  coal-tar  products.     Indigo  is  insoluble  in 
water,  but  can  be  suspended  in  it  in  the  same  way  as  ultra- 
marine.    By  treatment  with  fuming  sulphuric  acid  it  can 
be  converted   into   indigo   carmine    (sulphindigotic   acid},  a 
soluble  product  retaining  the  blue  color.     It  is  not  decolor- 
ized by  acids,  soap,  or  soda,  and  is  fast  to  light.    Suspended 
indigo  can  be  decolorized  by  treatment  with  sodium  bisul- 
phite and  zinc  dust,  indigo  carmine  by  sodium  bisulphite 
alone.     , 

3.  Soluble  Coal-tar  Products.  —  Blues  of  this  class  can 
often  be  recognized  by  making  one  portion  of  the  solution 
acid  and  another  alkaline  and  comparing  colors.     The  two 
will  usually  differ  in  shade.     The  best  coal-tar  blues  are  not 
actual  dyes,  which  would  permanently  color  the  textile,  but 
rather  substances  which  will   readily  wash    out,   e.g.    the 
alkali  blues  and  indigo  carmine. 

All  the  above  are  good  stable  blues.     The  soluble  blues  — 


BLEACHING  AND   BLUEING  253 

including  indigo  carmine  —  have  the  advantage  over  the  in- 
soluble that  they  give  a  more  even  coloring  to  the  fabric. 
Some  of  them,  however,  are  treated  with  oxalic  acid  in  the 
laundry  to  set  them  in  the  goods,  and  the  acid,  drying  in 
the  fabric,  corrodes  the  textile  fibers. 

A  cheap  but  very  objectionable  laundry  blue  is  Prussian, 
or  Berlin,  blue.  This  is  a  compound  of  iron,  carbon,  and 
nitrogen,  the  chemical  name  for  which  is  ferric  ferrocyanide. 
It  is  decomposed  by  alkalies  with  production  of  ferric  hy- 
droxide, Fe(OH)3.  Goods  treated  with  it  are  apt  to  show 
rust  stains,  particularly  if  they  contain  any  soap  or  soda 
when  blued. 

Experiment  165. 

Materials  : 
Ultramarine. 
Prussian  blue. 
Indigo. 
Soluble  blues. 
Soap  solution. 

Place  a  minute  quantity  of  each  blue  in  a  separate  test  tube. 
Fill  with  water  and  shake  until  the  blue  is  evenly  distributed 
through  the  water. 

Test  portions  of  each  liquid  with  the  following  solutions: 
(a)  Dilute  hydrochloric  acid.    Note  the  odor  from  the  ultramarine. 
Moisten  a  piece  of  filter  paper  with  lead  acetate  solution  and  hold 
at  the  mouth  of  the  test  tube. 

(6)  Sodium  hydroxide.  Compare  the  colors  with  those  of  the 
acidified  solutions  from  (a). 

(c)  Sodium  carbonate. 

(d)  Soap,  boiling. 

Allow  the  main  portions  to  stand  for  a  few  days  and  note  which 
form  sediments. 


CHAPTER  XLIII 

DYEING 

DYEING  consists  in  attaching  a  colored  substance  to  the 
fibers  of  the  textile  in  such  a  manner  that  it  is  not  -readily 
removed  by  rubbing  or  washing.  Whether  dyeing  involves 
a  chemical  union  between  the  fiber  and  the  coloring  matter 
is  a  disputed  question.  There  are  some  facts  which  appear 
to  indicate  that  such  combinations  of  fiber  and  dye  do  occur 
in  some  instances.  The  animal  fibers  (and  leather),  being 
protein  and  having,  therefore,  basic  and  acid  radicles,  will 
combine  directly  with  certain  dyes  which  are  acid  and  basic, 
whereas  the  same  dyes  will  not  become  attached  to  the  vege- 
table fibers.  On  the  other  hand,  the  product  of  the  deposi- 
tion of  the  dye  in  the  fiber  does  not  appear  to  have  properties 
distinct  from  those  of  the  dye  and  of  the  fiber,  which  ought 
to  Be  the  case  if  actual  combination  has  occurred ;  nor  does 
the  combination  seem  to  occur  in  the  definite  proportions  in 
which  substances  react  in  chemical  processes,  but  this  may 
be  because  the  enormous  size  of  the  protein  molecules  makes 
possible  an  almost  unlimited  number  of  compounds.  The 
fact  that  cotton  fibers  from  which  the  lumen  is  absent  refuse 
to  take  dyes  furnishes  another  argument  in  favor  of  a  physical 
theory  of  dyeing. 

The  protein  fibers  are  so  different  in  character  from  the 
cellulose  fibers,  and  the  diversity  of  chemical  nature  among 
dyestuffs  is  so  great,  that  it  is  not  likely  that  all  cases  of  dye- 
ing can  be  explained  in  the  same  way.  Physical  phenomena 
may  play  the  more  important  part  in  some  instances,  chemi- 
cal phenomena  in  others. 

Many  dyes  that  will  not  attach  themselves  directly  to^a 

254 


DYEING  255 

given  kind  of  fiber  will  dye  the  fiber  after  it  has  been  first 
treated  with  a  substance  called  a  mordant  (from  the  Latin, 
mordeo,  I  bite).  The  mordant  is  used  to  attach  to  the 
fiber  a  compound  capable  of  combining  with  the  dye  to  form 
an  insoluble  product.  The  insoluble  product  is  known  as  a 
lake. 

A  dye  that  will  dye  fibers  without  the  intervention  of  a 
mordant  is  called  a  substantive  dye. 

A  dye  that  will  only  attach  itself  to  the  fiber  through  the 
intervention  of  a  mordant  is  called  an  adjective  or  mordant 
dye. 

Practically  all  the  modern  dyes  are  organic  compounds. 
A  buff  color  of  iron  oxide  is  sometimes  produced  by  treating 
the  fabric  first  with  an  iron  solution  (such  as  ferrous  sulphate), 
then  with  an  alkali  (e.g.  sodium  hydroxide  or  sodium  car- 
bonate), and  then  exposing  it  to  the  air  to  oxidize  the  ferrous 
hydroxide,  Fe(OH)2,  formed  at  first,  to  ferric  hydroxide, 
Fe(OH)3.  "  Khaki  "  is  obtained  by  adding  a  chromium  salt 
(chrome  alum)  to  the  iron  solution  and  treating  in  this  way, 
thus  producing  a  mixture  of  ferric  and  chromic  oxides.  Man- 
ganese brown,  composed  of  an  oxide  (or  hydroxide)  of  man- 
ganese, can  be  similarly  produced  from  solutions  of  manganese 
salts.  Chrome  yellow  is  produced  as  a  precipitate  in  the 
fibers  when  the  goods  are  treated  first  with  lead  acetate  and 
then  with  potassium  dichromate.  These  inorganic  dyes  are 
sometimes  called  "  mineral  pigments." 

Of  the  organic  dyes  a  few  are  still  obtained  from  plant  or 
animal  sources.  Logwood,  a  dye  extracted  from  the^  heart 
wood  of  a  large  South  and  Central  American  tree,  the  Haema- 
toxylon  campechianum  (literally,  blood-red  wood  of  Campeachy), 
is  used  extensively  in  the  silk  industry  and  in  calico  printing 
for  the  production  of  a  full  black.  Quercitrin  bark  and  Per- 
sian berry  are  still  used  in  dyeing  yellow,  although  better 
effects  are,  as  a  rule,  obtained  with  synthetic  dyes. 

Natural  indigo,  obtained  by  exposing  to  the  air  the  juice 


256  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

of  the  leaves  of  various  species  of  plants  of  the  genus  Indigo- 
fera,  formerly  cultivated  on  a  large  scale  in  India,  has  within 
the  last  decade  been  almost  entirely  replaced  by  synthetic 
indigo,  the  same  compound  in  purer  form  manufactured 
from  coal-tar  products. 

Madder,  obtained  from  the  dried  roots  of  the  madder  plant 
and  used  for  the  production  of  Turkey  red,  has  long  been 
replaced  by  synthetic  alizarin,  a  compound  identical  with 
one  of  those  contained  in  the  natural  product.  Alizarin  is 
manufactured  from  coal-tar  products,  and  derivatives  of  the 
compound  are  in  use  which  enable  the  dyer  to  obtain  blues, 
purples,  yellows,  etc.,  chemically  similar  to  Turkey  red  and 
equally  fast  to  light  and  washing.  Such  vegetable  dyes  as 
sandalwood,  archil,  alkanet,  fustic,  turmeric,  and  cudbear, 
and  such  insect  dyes  as  cochineal,  kermes,  and  lac  dye,  have 
been  replaced  almost  completely  by  coal-tar  derivatives,  not 
identical  with  the  natural  coloring  matter  of  these  sub- 
stances, but  superior  to  them  in  fastness,  in  convenience,  in 
economy,  or  in  beauty.  Cochineal,  however,  is  still  used  to 
some  extent. 

The  synthetic  (i.e.  built-up)  dyes  are  all  derived  from 
products  of  coal  tar.  The  first  to  be  manufactured  were 
made  from  aniline,  C6H5NH2,  and  the  term  "  aniline  dyes  " 
is  sometimes  applied  in  popular  language  to  the  whole  group 
of  substances.  Only  a  few  of  them,  however,  are  actually 
made  from  aniline.  Coal-tar  dyes  and  synthetic  dyes  are  more 
appropriate  names  for  the  class.  Coal  tar  is  obtained  as  a 
by-product  when  coal  is  heated  out  of  contact  with  air, 
which  is  done  in  the  manufacture  of  coke  for  fuel  and  coal 
gas  for  illuminating  purposes.  (See  Chapter  XII.)  The 
tar  is  a  mixture  of  an  enormous  number  of  organic  com- 
pounds. Prominent  among  them  are  the  hydrocarbons 
benzene,  C6H6,  naphthalene,  CioHg,  and  anthracene,  CuHio ; 
the  phenols,  carbolic  acid  (phenol  proper),  C6H5OH,  and 
the  three  cresols,  CrHyOH ;  and  the  amine,  aniline, 


DYEING  257 

From  these  coal-tar  products  are  derived,  directly  or  in- 
directly, thousands  of  chemical  compounds,  among  which 
are  many  coloring  matters.  Of  these  a  considerable  num- 
ber make  good  dyes. 

The  coal-tar  dyes  may  be  classified  as  follows  : 

1.  Direct  or  Substantive  Cotton  Dyes. 

2.  Developed  Dyes. 

3.  Mordant  or  Adjective  Dyes. 

4.  Acid  Dyes. 

5.  Basic  Dyes. 

i.   Direct  or  Substantive  Cotton  Dyes 

These  dye  cotton  without  the  intervention  of  a  mordant. 
Their  application  is  so  simple  and  inexpensive  that  they  are 
very  commonly  used,  although  as  a  class  they  are  excelled 
in  fastness  by  the  mordant  dyes  and  in  brilliance  by  the 
basic  colors.  The  transfer  of  dyes  of  this  class  from  solution 
to  the  fibers  is  accelerated  by  the  addition  of  salts,  especially 
sodium  chloride  and  sodium  sulphate,  to  the  solution. 
Hence  the  name  "  salt  colors  "  sometimes  applied  to  this 
class  of  dyes.  Alkalies,  on  the  other  hand,  tend  to  retard  the 
precipitation  of  the  coloring  matter  into  the  fiber.  Sodium 
carbonate,  sodium  phosphate,  and  soap  are  sometimes  added 
to  the  bath  to  render  the  dyeing  slower  and  more  penetrative. 

In  washing  goods  dyed  with  dyes  of  this  class  the  soda 
and  soap  used  tend  to  cause  "  bleeding  "  of  the  dye,  while 
salt  added  to  the  water  will  sometimes  prevent  this  trouble. 
In  many  instances  the  fastness  of  a  substantive  dye  to  wash- 
ing is  improved  by  after  treatment  with  metallic  salts  or  with 
formaldehyde. 

In  other  instances  the  material  originally  deposited  is  con- 
verted into  another  and  faster  dye  by  a  developing  process. 
Many  of  the  dyestuffs  contain  amino  ( — NHo)  groups,  and 
it  is  these  which  are  used  for  this  purpose.  After  the  sub- 


258  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

stantive  dye  containing  an  amino  group  is  applied,  the 
goods  are  treated  with  nitrous  acid  (HNOs).  This  reagent 
converts  the  amines  in  the  fiber  into  unstable  compounds 
known  as  diazonium  salts.  The  conversion  of  an  amine  into 
a  diazonium  salt  is  called  diazotizing.  When  a  diazonium 
salt  is  brought  into  a  solution  containing  another  amine  or  a 
phenol,  a  reaction  takes  place  by  which  the  molecule  of  the 
amine  or  phenol  is  combined  with  that  of  the  substantive  dye 
through  two  nitrogen  atoms,  the  product  being  a  dye  faster 
than  that  originally  applied  and  sometimes  also  of  a  different 
color.  The  yellow  dye,  primuline,  for  instance,  can  be  de- 
veloped into  a  red  dye  by  diazotizing  and  coupling  with 
/8-naphthol. 

Experiment  166.  —  Dyeing  Cotton  with  a  Substantive  Dye. 

Materials : 

Skein  of  cotton  yarn. 
Primuline. 
Salt. 

Dissolve  0.3  gram  of  primuline  and  i  gram  of  salt  in  just 
sufficient  water  to  cover  5  grams  of  the  cotton.  Add  about  |  cc. 
sodium  carbonate  solution.  Heat  to  60°  C.  (140°  F.),  introduce 
the  5  grams  of  cotton,  and  gradually  heat  to  boiling.  Boil  1 5  to 
30  minutes.  Note  the  color.  Rinse  in  cold  water. 

Experiment  167.  —  Development  of  a  Substantive  Dye  by  Diaz- 
otizing. 

Materials : 

Dyed  skein  of  cotton  from  preceding  experiment. 
Sodium  nitrite. 
/8-naphthol. 

Dissolve  0.25  gram  sodium  nitrite  in  sufficient  water  to  cover 
the  goods.  Add  3  cc.  dilute  sulphuric  acid.  What  acid  is  pro- 
duced? Immerse  the  dyed  skein  of  cotton  for  10  minutes,  keeping 
the  bath  cool.  Does  the  color  change? 

Rinse  in  acidulated  water  and  immediately  transfer  to  a  bath 
containing  o.i  gram  0-naphthol  dissolved  in  an  equal  weight  of 
a  30  per  cent  solution  of  NaOH.  Note  the  production  of  the  new 
color. 


DYEING  259 

Although  called  direct  cotton  dyes,  many  of  this  class  give 
even  better  results  on  wool.  This  is  especially  true  of  the 
reds  and  yellows. 

Closely  related  to  the  substantive  dyes,  at  least  in  the 
manner  of  their  application,  are  the  so-called  "  sulphur 
dyes."  These  are  applied  in  a  salt  bath  to  which  sodium 
sulphide  has  been  added.  They  are  used  exclusively  on 
cotton  and  linen.  They  are  exceedingly  fast  to  washing. 

2.   Developed  Dyes 

The  developed  dyes  are  those  whose  colors  are  produced 
within  the  fiber.  They  may  be  produced  (a)  by  oxidation 
of  a  soluble  compound  to  an  insoluble  dye  or  (6)  by  combin- 
ing two  colorless  or  slightly  colored  compounds  into  a  dye  by 
diazotizing. 

The  "  vat "  dyes  and  aniline  black  are  examples  of  the 
first  class.  The  vat  dyes,  of  which  indigo  is  the  oldest  ex- 
ample, are  reduced  to  so-called  "  leuco  compounds  "  by  strong 
reducing  agents.  The  leuco  compounds,  being  soluble,  pene- 
trate the  fiber.  The  goods  are  then  exposed  to  air  for 
15  to  20  minutes,  after  which  they  are  boiled  in  a  soap  solu- 
tion. This  treatment  reoxidizes  the  leuco  compound  to  the 
insoluble  dye.  The  vat  colors  are  characterized  by  extreme 
fastness,  not  only  to  light  and  washing,  but  also  to  the  action 
of  acids,  alkalies,  and  oxidizing  agents. 

The  reduction  of  indigo  was  formerly  accomplished  by  a 
fermentation,  whence  the  term  "  vat."  The  reducing  agent 
now  almost  universally  used  for  all  vat  colors  is  sodium  hydrc- 
sulphite,  Na2S2O4,  which  is  prepared  by  reducing  sodium 
bisulphite  with  zinc  dust.  Sodium  hydrosulphite  is  very 
readily  oxidized  by  the  oxygen  of  the  air.  A  compound  of 
sodium  hydrosulphite  with  formaldehyde,  which  is  less 
affected  by  the  air,  is  sometimes  used  instead  of  the  sodium 
hydrosulphite  itself. 


260  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

Experiment  168. — Vat  Dyeing  with  Indigo. 

Materials : 

Sodium  bisulphite  solution  (30  per  cent)  and  zinc  dust. 
Indigo  powder  or  paste. 
Sodium  hydroxide  (30  per  cent). 
Cotton  skein  or  piece  of  cheesecloth. 

To  i  gram  zinc  dust  in  a  test  tube  add  10  cc.  of  the  sodium 
bisulphite  solution.  Allow  to  stand  for  a  few  minutes,  stirring 
gently  from  time  to  time  with  a  glass  rod.  The  sediment  should 
become  pale  gray.  What  compound  is  produced  by  this  action  ? 

In  another  test  tube  place  i  gram  powdered  indigo  or  2.5  grams 
indigo  paste,  20  per  cent.  Add  8  cc.  of  the  concentrated  sodium 
hydroxide  solution  and  mix.  Add  the  contents  of  the  other  tube, 
heat  to  50°  C.  (120°  F.),  and  set  in  a  beaker  of  water  at  50°  C. 
Allow  to  stand  until  the  material  has  turned  yellow  (about  \  hour). 
Sufficient  material  is  obtained  for  3  or  4  students  to  perform  the 
actual  dyeing,  which  is  done  as  follows : 

Into  50  cc.  water  put  a  very  little  zinc  dust  (o.i  gram)  and  sodium 
bisulphite  solution  (0.5  cc.).  This  removes  the  dissolved  oxygen 
from  the  water.  Add  about  one  fourth  of  the  yellow  liquid.  Wet 
the  cotton,  immerse  it  for  a  minute  or  so,  squeeze  it  out  well,  and 
hang  it  exposed  to  the  air  for  5  or  10  minutes.  Note  the  develop- 
ment of  the  color.  Rinse  with  water,  soap  to  remove  unabsorbed 
dye,  and  rinse  again. 

Sodium  hydrosulphite,  or  its  formaldehyde  compound,  may  be 
used  instead  of  the  zinc  and  sodium  bisulphite.  Use  2  grams 
sodium  hydrosulphite  and  20  cc.  water  for  2  grams  indigo,  and 
allow  to  stand  10  minutes  before  adding  the  sodium  hydroxide, 
of  which  only  half  as  much  will  be  required  as  when  the  bisulphite 
is  used.  Heat  to  60°  C.  (140°  F.)  and  allow  to  stand  until  a  glass 
rod  dipped  into  the  mixture  gives  a  clear  yellow  drop  and  the 
liquid  wetting  the  rod  becomes  blue  after  about  half  a  minute's 
exposure  to  the  air.  A  little  hydrosulphite  should  be  used  to 
remove  the  dissolved  oxygen  from  the  diluting  water. 

Aniline  black  is  a  color  so  fast  to  washing  that  it  forms 
the  basis  of  many  marking  inks.  It  is  an  oxidation  product 
of  aniline,  C6H5NH2,  produced  not  by  the  action  of  atmos- 
pheric oxygen,  but  by  that  of  oxidizing  agents.  Pure  aniline 
is  a  colorless,  oily  liquid,  insoluble  (or  rather  only  slightly 
soluble)  in  water,  and  possessed  of  a  penetrating,  somewhat 


DYEING  261 

nauseating  odor.  The  ordinary  "  aniline  oil  "  of  commerce 
is,  however,  colored  yellowish  brown  by  impurities.  Being 
an  amine,  aniline  forms  salts  with  acids,  similar  to  the 
ammonium  salts,  e.g.  aniline  hydrochloride,  CeHsNHaCl. 
These  salts  are  soluble  in  water.  In  dyeing  with  aniline 
black  the  goods  are  impregnated  with  an  oxidizing  agent 
such  as  potassium  (or  sodium)  chlorate,  with  an  aniline  salt, 
and  with  a  catalytic  agent,  such  as  copper  sulphate  or  sodium 
ferrocyanide.  They  are  then  exposed  to  the  action  of  steam 
for  half  a  minute  and  afterwards  treated  with  soap.  The 
heat  and  moisture  promote  the  oxidation.  Aniline  black 
can  also  be  obtained  directly  from  aniline  by  oxidizing  it 
with  a  mixture  of  potassium  dichromate  and  sulphuric  acid, 
as  in  the  following  experiment. 

Experiment  169.  —  Dyeing  with  Aniline  Black. 

Materials  : 

Aniline  oil.  « 

Potassium  dichromate  solution  (5  per  cent). 
Cotton  skein  or  cheesecloth. 

Note  odor  and  appearance  of  commercial  aniline.  Shake  about 
i  cc.  with  water  (5  cc.).  Add  concentrated  hydrochloric  acid  and 
shake  again. 

To  100  cc.  potassium  dichromate  solution  add  250  cc.  water 
and  10  cc.  dilute  (2  N.)  sulphuric  acid.  Dissolve  if  cc.  aniline 
in  2^  cc.  concentrated  hydrochloric  acid  and  add  to  the  dichromate 
mixture.  Immerse  the  cotton  and  slowly  heat  the  bath  to  80°  C. 
(175°  F.).  Rinse  well,  soap,  wring  out,  and  dry  without  rinsing 
out  the  soap. 

On  account  of  the  use  of  the  strong  "  mineral  "  acids, 
aniline  black  dyeing  is  apt  to  injure  the  fiber.  The  use  of 
sodium  (or  potassium)  ferrocyanide,  Na4Fe(CN)  6,as  a  catalytic 
agent  appears  to  mitigate  this  evil.  It  reacts  with  the  mineral 
acid,  e.g.  hydrochloric,  giving  sodium  chloride  and  ferro- 
cyanic  acid,  H4Fe(CN)6,  a  weaker  acid  than  hydrochloric. 

The  second  class  of  developed  synthetic  dyes  embraces 


262  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

those  which  are  produced  by  saturating  the  goods  with  the 
solution  of  a  colorless  compound  (technically  a  "  prepare  "), 
then  introducing  them  into  a  diazotized  solution  of  an  amine 
—  in  other  words,  into  the  solution  of  a  diazonium  salt.  The 
principle  is  exactly  the  same  as  that  of  the  after- development 
of  substantive  colors,  described  above  (p.  257),  and  the 
product  is  an  insoluble  dye,  precipitated  within  the  fiber. 
The  diazonium  salts  are  only  stable  at  low  temperatures. 
Ice  is  therefore  kept  in  the  developing  solution.  On  account 
of  this  circumstance  colors  produced  by  this  process  are 
called  "  ice  colors." 

The  "  prepare  "  universally  used  for  ice  colors  is  a  solution 
of  sodium  /?-naphtholate,  prepared  by  dissolving  /3-naphthol 
in  caustic  soda.  Several  beautiful  reds  are  produced  by  this 
process,  and  blue  and  black  can  also  be  obtained. 

Experiment  170.  —  Dyeing  with  Paranitraniline  Red. 

Materials : 

Skein  of  white  cotton  yarn  or  piece  of  cheesecloth. 

Paranitraniline. 

/3-naphthol. 

Sodium  nitrite. 

Sodium  acetate  crystals. 

Sodium  hydroxide  solution  (30  per  cent). 

Dissolve  3  grams  /3-naphthol  in  100  cc.  water  to  which  have  been 
added  3  cc.  of  the  strong  sodium  hydroxide  solution. 

In  a  250  cc.  beaker,  heat  7  grams  paranitraniline  with  4  cc.  cone, 
hydrochloric  acid  and  75  cc.  water.  Paranitraniline  hydrochloride 
is  formed.  When  all  has  dissolved,  cool  quickly,  stirring  rapidly 
so  as  to  make  the  hydrochloride  crystallize  out  in  small  crystals. 
Continue  the  cooling  below  the  room  temperature  by  putting  ice 
into  the  beaker.  When  the  temperature  reaches  4°  C.  (39  to 
40°  F.),  gradually  add  4  cc.  concentrated  hydrochloric  acid,  then 
throw  in  3.5  grams  sodium  nitrite.  Keep  down  to  4°  C.  by  adding 
more  ice  as  needed.  After  10  or  15  minutes  add  8  grams  sodium 
acetate  crystals. 

Immerse  the  cotton  in  the  /3-naphthol  "  prepare,"  wring  out 
gently,  dry  carefully,  and  immerse  in  the  cold  diazonium  salt 
solution.  Work  the  cotton  in  the  solution  for  a  minute  or  so. 


DYEING  263 

Remove,  rinse  well,  dip  into  water  to  which  a  little  sodium  car- 
bonate has  been  added,  then  rinse  again  thoroughly. 

Instead  of  the  paranitraniline  the  following  may  be  used  in  the 
experiment,  the  red  colors  obtained  varying  in  shade  from  para- 
nitraniline red:  a-naphthylamine  (7  grams),  /3-naphthylamine 
(7  grams),  benzidine  (4.5  grams),  metanitraniline  (7  grams). 

3.   Mordant  or  Adjective  Dyes 

The  mordant  or  adjective  dyes  may  be  either  of  acid  or  of 
basic  character.  In  the  case  of  the  acid  dyestuffs  the  mor- 
dants used  are  of  such  a  character  that  they  leave  upon  the 
fiber,  and  firmly  combined  with  it,  metallic  bases  which  are 
capable  of  combining  with  the  acid  dyestuff.  Soluble  salts 
or  soluble  basic  salts  of  the  weak  bases  are  suitable.  Those 
used  practically  are  salts  of  aluminium,  iron,  chromium,  tin, 
copper,  cobalt,  and  nickel.  The  goods  are  immersed  in  solu- 
tions of  the  salts  and  then  either  subjected  to  the  action  of  a 
weak  alkali,  or,  in  case  the  acid  of  the  salt  is  a  volatile  one, 
are  steamed  to  liberate  the  weak  acid  and  drive  it  off  as  vapor. 

As  a  rule,  goods  prior  to  drying  are  subjected  to  the  process 
of  "  dunging,"  which  in  the  practice  of  half  .-a  century  ago 
consisted  in  passing  the  goods  through  cow  dung.  Later, 
arsenate  of  soda  was  substituted,  but  phosphate  of  soda  has 
now  superseded  this  poisonous  compound.  The  effect  of 
the  dunging  process  is  to  fix  the  mordant  more  firmly  in  the 
fiber  and  thus  enhance  the  fastness  of  the  dye  subsequently 
to  be  applied.  The  dunging  process  has  also  the  effect  of 
removing  the  surplus  mordant  so  as  to  insure  an  even  surface 
of  the  goods  ("level  dyeing").  Afterwards  the  goods  are 
dyed,  the  dyestuff  combining  with  the  metallic  base  to  form 
a  lake,  often  different  in  color  from  the  dyestuff  itself. 

Experiment  151.  — Alizarin  Lakes. 

Materials : 

Alizarin. 

Solutions  of  aluminium,  chromium,  and  ferrous  salts. 
Dissolve  a  little  alizarin  in   ammonia.    To  separate  portions 


264  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

of  the  solution,  add  calcium  sulphate  and  small  quantities  of  the 
aluminium,  chromium,  and  ferrous  solutions.  Heat  to  boiling 
and  filter.  Note  the  colors  of  the  precipitates.  Wash  them  on 
the  filter.  Do  they  retain  the  dye? 

For  comparison  precipitate  the  hydroxides  of  the  metals  by 
adding  ammonium  hydroxide  to  the  solutions. 

As  an  auxiliary  to  the  mordant  base,  an  acid  mordant  or 
fixing  agent  is  sometimes  employed.  The  leading  examples 
of  this  class  of  bodies  are :  (i)  the  tannins,  (2)  fatty  acid  deriva- 
tives. The  tannins  or  tannic  acids  are  much  used  with  the 
basic  dyes  (see  below)  and  as  weighting  agents  for  silk.  (See 
Chapter  XL.)  Cotton  which  is  to  be  mordanted  with  iron, 
tin,  or  aluminium  salts  is  sometimes  first  treated  with  a  tan- 
nin, usually  sumac  extract. 

The  most  important  fatty  acid  derivative  used  as  a  fixing 
agent  is  Turkey-red  oil.  This  is  prepared  by  treating  castor 
oil  or  olive  oil  with  concentrated  sulphuric  acid,  keeping  the 
mixture  cold.  The  product  is  soluble  in  water,  but  it  is  cus- 
tomary to  partially  neutralize  with  caustic  soda  or  ammonia 
to  render  it  more  soluble.  It  takes  its  name  from  its  use  in 
Turkey-red  dyeing.  The  dye  used  in  this  process  is  alizarin, 
and  before  the  discovery  of  Turkey-red  oil  the  mordanting 
of  the  cotton,  preliminary  to  dyeing  with  extract  of  madder 
root,  was  a  very  lengthy  process,  requiring  several  weeks 
for  its  completion.  Nowadays  the  goods  are  treated  with 
Turkey-red  oil,  dried  overnight,  mordanted  in  an  aluminium 
solution,  dried  again  overnight,  treated  with  a  mild  alkali 
(usually  chalk),  dyed  with  synthetic  alizarin,  steamed, 
soaped,  rinsed,  and  dried.  The  whole  process  is  completed 
in  three  days,  and  the  result  compares  favorably  with  that 
obtained  by  the  old  process.  Slightly  rancid  olive  oil  and 
soaps  containing  a  little  free  fatty  acid  are  other  materials 
used  with  alizarin  and  dyes  chemically  related  to  it.  Some- 
times tannins  and  fatty  acid  fixing  agents  are  both  used  with 
these  dyes. 


DYEING  265 

4.  Acid  Dyes 

The  acid  dyes  dye  wool  and  silk  directly.  They  are  very 
seldom  used  on  cotton.  They  are  usually  sold  in  the  form 
of  their  sodium  salts,  and  are  liberated  in  the  dyeing  bath  by 
treatment  with  an  acid,  usually  sulphuric.  Sodium  sulphate 
is  used  as  a  restraining  agent,  preventing  too  rapid  absorp- 
tion of  the  dye.  This  is  just  the  opposite  effect  from  that 
played  by  sodium  sulphate  in  dyeing  cotton  with  direct  dyes. 

There  is  great  variety  among  the  acid  dyes,  and  they  play 
a  very  important  part  in  the  dyeing  of  wool  and  silk.  The 
best  of  them  are  very  fast  to  light,  although  not  equal  to  the 
vat  dyes  in  this  respect.  They  are  not  fast  to  washing  with 
soap. 

5.  Basic  Dyes 

The  basic  dyes,  which  are  the  real  aniline  derivatives,  are 
applied  to  wool  and  leather  directly  (rarely  to  silk)  and  to 
cotton  mordanted  with  tannin.  Chardonnet  artificial  silk 
(p.  239)  takes  these  dyes  better  than  those  of  any  other  class. 
They  are  characterized  by  great  brilliance,  but  very  few  of 
them  are  fast  to  light.  In  cotton  dyeing  they  are  often  used 
to  "  top  "  other  dyes.  The  brightness  of  sulphur  dyes  can 
be  increased  by  such  topping,  and  so  also  can  the  fastness  of 
the  substantive  dyes  to  washing. 

The  chief  tannins  used  as  mordants  or  fixing  agents  for 
the  basic  dyes  are  those  derived  from:  (i)  gallnuts,  which 
are  excrescences  produced  on  oak  trees  and  other  plants  as 
the  result  of  insect  injuries;  (2)  sumac  leaves  and  twigs; 
(3)  catechu;  (4)  horse-chestnut  wood.  Cotton  immersed  in 
tannin  solutions  absorbs  more  or  less  of  the  tannins.  The 
tannin  behaves  as  an  acid,  weak  but  polybasic,  i.e.  having 
several  replaceable  hydrogen  atoms.  The  cotton  is  next 
treated  with  an  antimony  salt,  usually  potassium  antimonyl 
tartrate,  tartar  emetic.  An  insoluble  antimony  tannate,  or 
acid  antimony  tannate,  is  produced  in  the  fiber,  and  this  has 


266  ELEMENTARY    HOUSEHOLD    CHEMISTRY 

sufficient  replaceable  hydrogen  left  to  act  as  an  acid  towards 
the  basic  dye.  In  dyeing,  a  double  tannate  of  antimony  and 
the  dyestuff  is  formed  in  the  fiber. 

Calico  Printing 

Designs  on  cotton  are  produced  by  means  of  printing 
machines,  which  consist  essentially  of  rollers  upon  which 
the  design,  or  so  much  of  it  as  is  to  be  printed  in  one  color, 
is  engraved.  The  rollers  may  be  employed  either  (i)  to 
apply  the  dyestuff,  thickened  with  starch  or  gum,  directly 
to  the  goods,  (2)  to  print  upon  the  goods  a  mordant  which 
will  fix  a  dye  to  be  subsequently  applied,  (3)  to  print  upon 
the  goods  a  reagent  which  will  resist  the  action  of  a  dye  to 
be  subsequently  applied,  (4)  to  print  upon  dyed  goods  a  re- 
agent which  will  discharge  the  dye  by  converting  it  into  a 
colorless  compound,  or  by  removing  the  mordant  which 
holds  the  dye,  or  (5)  to  print  both  a  discharging  agent  and  a 
new  dye  or  mordant. 

Practically  all  the  dyes  which  are  applicable  to  cotton  can 
be  used  in  printing  processes. 


APPENDIX  A 
LIST  OF  TABLES  IN  APPENDIX  A 

Table  Subject 

I.   Foods  of  Vegetable  Origin  —  Average  Composition  and 

Nutritive  Value. 

II.  Foods  of  Vegetable  Origin  —  Important  Ash  Constitu- 
ents in  the  One-Hundred-Calorie  Portion  of  Edible 
Material. 

III.  Foods  of  Animal  Origin — Meats — Average  Composition 

and  Nutritive  Values. 

IV.  Foods  of  Animal  Origin  —  Composition  of  Meats,  Fat 

and  Lean. 
V.   Foods  of  Animal  Origin  —  Fish  —  Average  Composition 

and  Nutritive  Value. 
VI.   Foods  of  Animal  Origin  —  Dairy  Products  —  Average 

Composition  and  Nutritive  Value. 

VII.   Miscellaneous  Foods  of  Animal  Origin  —  Average  Com- 
positions and  Nutritive  Value. 

VIII.  Foods  of  Animal  Origin  —  Important  Ash  Constituents 
in  the  One-Hundred-Calorie  Portion  of  Edible 
Material. 

IX.  Approximate  Weights  of  One  Cupful  of  Some  Food 
Materials. 

TABLES 

The  following  tables  of  food  composition  are  derived,  for  the 
most  part,  from  the  compilations  of  Atwater  and  Bryant,1  of 
Sherman,2  and  of  Rose.3 

1  Atwater  and  Bryant,  "  Chemical  Composition  of  American  Food  Materi- 
als," Office  of  Experiment  Stations,  United  States  Department  of  Agriculture, 
Bulletin  28,  Revised  edition,  1899.     These  tables  are  also  to  be  found  in  the 
appendix  to  Jordan's  "  Principles  of  Human  Nutrition,"  New  York,  1912. 

2  Sherman,  "  Chemistry  of  Food  and  Nutrition,"  New  York,  1911. 

3  Rose,  "  A  Laboratory  Hand-Book  for  Dietetics,"  New  York,  1913. 

267 


268  APPENDIX  A 

NOTE.  In  the  tables  of  Atwater  and  Bryant  (Bulletin  28)  and  in  the  data 
drawn  from  them  by  Jordan,  the  fuel  values  are  calculated  by  factors  which 
are  now  known  to  have  allowed  too  little  for  losses  in  digestion  and  which 
gave  results  from  2.5  to  3.3  per  cent  too  high.  The  fuel  values  given  here  (as 
well  as  those  in  the  tables  of  Sherman  and  of  Rose)  are  recalculated  by  the  later 
and  more  accurate  factors  as  given  in  the  foregoing  text ;  viz.  protein  and 
carbohydrate,  4  Calories  per  gram ;  fat,  9  Calories  per  gram.  These  factors 
are  equivalent  to  1814  Calories  per  pound  for  protein  and  carbohydrates  and 
4082  Calories  per  pound  for  fat.  The  fuel  values  in  the  tables  are  calculated 
to  the  nearest  5  Calories  and,  consequently,  do  not  coincide  exactly  with  those 
given  by  Sherman  and  by  Rose. 

Table  I  gives  the  composition  and  nutritive  value  of  selected  foods 
of  vegetable  origin,  arranged  in  groups,  and  Tables  III- VII  those  of 
selected  foods  of  animal  origin.  In  these  tables  there  is  first  given 
the  per  cent  of  refuse  —  peel  and  stems  of  fruit,  bone  and  tendons 
of  meat,  etc.,  in  short  all  the  material  that  is  not  usable  as  food. 
The  remaining  columns  all  refer  to  the  edible  portion  of  the  food. 
The  percentage  composition  of  the  edible  portion  (omitting  the 
ash)  is  next  given,  then  fuel  value  in  calories  per  pound. 

From  these  data  the  remaining  figures  of  the  tables  are  cal- 
culated as  follows  : 

i.  The  one  hundred  Calorie  portion  in  ounces  by  dividing  1600 
by  the  fuel  value  per  pound. 


EXAMPLES 
Bananas  1 


'-nanas l 

Fuel  value  per  pound  450  Calories 

450  Calories  are  yielded  by  16  ounces 

*.  100  Calories  are  yielded  by  1600  -f-  450  =  3.6  ounces 

itermelons  l 

Fuel  value  per  pound  135  Calories 

loo-Calorie  portion  in  ounces  1600  -=-  135  =  11.9 


Dates  1 

Fuel  value  per  pound        1575  Calories 
loo-Calorie  portion  in  ounces  1600  -f-  1575  =  1.02 

2.  The  distribution  of  the  100  Calories  by  multiplying  the  per 
cent  of  fat  by  2.25,  adding  the  per  cent  of  protein  and  the  per  cent 
of  carbohydrate,  dividing  the  sum  by  each  addend,  and  multiplying 
the  result  by  100. 

1  In  all  cases  the  data  given  relate  to  the  edible  portion  of  the  food. 


APPENDIX  A  269 

EXAMPLES 
Bananas 

Per  cent  of  fat  in  the  edible  portion  0.6 

0.6  Ib.  fat  is  equivalent   to   0.6  X  2.25  =  1.35  Ib.  protein  or 

carbohydrate 

Per  cent  of  protein  1.3 

Per  cent  of  carbohydrates  22.0 

Sum          24.65 
Out  of  every  24.65  Calories  the  protein  contributes  1.3 

Out  of  every  100  Calories  the  protein  contributes  -    — =  5, 

approximately 
Out  of  every  24.65  Calories  the  fat  contributes  1.35 

Out  of  every  100  Calories  the  fat  contributes  -     }-— =  6, 

approximately 

Out  of  every  24.65  Calories  the  carbohydrate  contributes  22.0 
Out    of    every    100    Calories    the     carbohydrate     contributes 

22.0  X  100 

=  89,  approximately 

24.65 

Olives 

Fat  27.6  per  cent,  equivalent  in 
fuel    value    to    27. 6X2. 25=       60. i   per   cent   protein  or 

carbohydrate 

Per  cent  of  protein  i.i 

Per  cent  of  carbohydrate  n.6 

Sum  72.8 

Out  of  72.8  Calories  the  proteins  yield  i.i 

Out  of  100  Calories  the  proteins  yield  —   =  1.5  Calories 

72.8 

Out  of  72.8  Calories  the  fats  yield  60. i 

Out  of  100  Calories  the  fats  yield  -  —  =  82.5 

72.8 

Out  of  72.8  Calories  the  carbohydrates  yield  n.6 

Out  of  100  Calories   the   carbohydrates  yield =  16 


270  APPENDIX  A 

Pork,  salt,  clear  fat 

Fat  86.2  per  cent,  equivalent  to  86.2  X  2.25  =  194.0  proteins  or 

carbohy- 
drates 

Protein  1.9 

Sum        195.9 
Out  of  195.9  Calories  proteins  yield  19 

Out  of  100  Calories  proteins  yield  — =  i  Calorie 

195-9 
Out  of  195.9  Calories  fats  yield  194.0 

Out  of  100  Calories  fats  yield '- =  99  Calories 

195-9 

Tables  II  and  VIII  give  for  foods  of  vegetable  and  of  animal 
origin,  respectively,  the  content  of  the  most  important  ash  con- 
stituents, the  foods  being  compared  on  the  basis  of  equal  fuel 
value.  Table  IV  gives  the  average  composition  of  lean  and  of 
fat  meats  of  the  same  varieties. 


APPENDIX  A 


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278  APPENDIX  A 

TABLE  II.  —  FOODS  OF  VEGETABLE  ORIGIN 

Important  Ash  Constituents  in  the  One-hundred-Calorie  Portion  of 
Edible  Material1 


100- 

CALORIE 
PORTION 
(EDIBLE) 


IMPORTANT  ASH  CONSTITUENTS 
PER  IOO-CALORIE  PORTION 


CaO 


FRUITS,  FRESH  Grams 

Bananas 101 

Grapes      .......  104 

Plums 118 

Cherries    .......  128 

Raspberries 151 

Pears 158 

Apples 159 

Oranges 195 

Lemons 226 

Peaches 242 

Strawberries 269 

Watermelons 332 

FRUITS,  DRIED 

Dates 29 

Raisins 29 

Currants,  Zante      ....  31 

Figs 32 

Prunes 33 

FRUITS,  SPECIALLY  USED 

For  Pickles 

Olives,  green      .....  33 

Cucumbers 575 

As  "  Vegetables  " 

Squashes 217 

Pumpkins 389 

Tomatoes 438 

ROOTS,  TUBERS,  AND  BULBS 

Sweet  potatoes 81 

Potatoes 1 20 

Parsnips 154 

Onions 206 

Beets    ........  217 


Mg. 
10 
24 
29 
40 

no 

32 

22 

no 

120 
2O 

130 
60 


30 

2O 
40 
89 
2O 


60 
I  2O 

40 

no 

87 

20 

19 
I4O 
1 2O 

60 


Mg. 

55 

1 20 

64 

90 

180 

90 

So 

90 

40 

162 
60 

30 
80 
90 

99 
80 


10 

450 

170 
420 

257 

80 
1 66 
290 
240 
190 


*  Not  determined. 

1  Selected  from  the  more  comprehensive  tables  of  Sherman, 
Food  and  Nutrition,"  pp.  338-341. 


;  Chemistry  of 


APPENDIX  A 


279 


TABLE  II.  —  FOODS  OF  VEGETABLE  ORIGIN.  —  Continued 


100- 

CALORIE 
PORTION 
(EDIBLE) 

IMPORTANT  ASH  CONSTITUENTS 
PER  IOO-CALORIE  PORTION 

CaO 

P2O6 

Fe 

Carrots     ."    . 

Grams 
221 
254 
341 

317 
328 
417 
450 
433 
525 
542 

IOO 

241 

28 
29 

223 

25 
28 
28 

29 
29 
28 
28 
38 
38 
'    4i 

14 
15 
18 

4i 

Mg. 
168 

222 
170 

214 
550 
370 
170 
260 
260 
540 

32 
177 

40 
63 

S3 

30 
4 
7 
3 
5 
17 
7 
J9 
ii 
16 

IS 
46 
18 
17 

Mg. 
220 
292 
300 

280 
450 
540 
390 
300 
470 
540 

240 
284 

250 
326 

530 

216 
80 
127 

57 
220 

253 
So 
190 

75 
1  60 

1  08 
132 
160  • 

80 

Mg. 
1.6 
i-3 

2.0 

3-5 

* 

13-3 

4-3 

* 

S-o 
2.7 

1.6 
3-8 

i-S  . 

2.0 
* 

0.9 

o-3 

0.4 

0-3 

* 

i-5 
0.4 

i-3 
0.3 
0.6 

0-3 
o-3 
0.4 
0.4 

Turnips                              *     . 

Radishes  , 

STALKS  AND  LEAVES 
Cabbage   
Cauliflower                        .     .  ' 

Spinach     

Asparagus      , 
Rhubarb  
Lettuce     . 
Celery                                .     .' 

LEGUMES,  GREEN 
Peas 

Beans  string 

LEGUMES,  RIPE 
Peas     
Beans 

FUNGI 
Mushrooms  

CEREAL  PRODUCTS 
Oatmeal    . 
Cornmeal                           .     . 

Barley,  pearled  ..... 

Rice     .                            .    . 

Rye  flour       ...... 
Wheat  flour,  Graham      .     . 
Wheat  flour,  white      .     .     . 
Bread,  Graham      .... 
Bread,  white  
Bread,  "  whole  wheat  "    .     . 

NUTS 
Walnuts   

Almonds 

Peanuts    ,     

Chestnuts      

*  Not  determined. 


280 


APPENDIX  A 


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P*-?«° 


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1 1 


•^•OHOO«N'J-        i^.  «o        rood 


w      'S 

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Mt^  IOOO 


M 


APPENDIX  A 


28l 


^*    OO     ^O    OO       ^     ^3"    ^  OO  *O    *O      O     M  OO    t^» 

O         O\CJ         M         fO    <N         O    O      rj-  00         O    (N     10    W 

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w" 

10 

fe     (N      M          (M       I         M      M      M  MC4MMMJ  M      <N       (N 

& 

|::::::::::::^ 

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-d  ^  .  P 

1|    i.a  ^  '1    •  •    .  £S    ....    -  •  -^ 

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X  | 


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4)       4) 

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282 


APPENDIX  A 


HHPOMMTJ-M<NTj-t^.<NCS<NTi-t~>.POThvO 


sf43 


jjvqoocor^Mi/-)    o1* 
|  d  d   H    d   M  H    d 


_  &•« 

&l 


S 


lOfO<SlO<NMfO<NM 


10  10 


H      <N      W      <N 


M       M       M       OJ          M 


>•§  -8 


-8  -i  2  •§  -8 


pq 


APPENDIX  A 


283 


u->    10   10   10   »0  10    CO    •>*•    -"3-    CO    ro  d     M     <N     M     M 


^r  ^r  ^r  ^r  ^       ^  o  lotovoo   oi>-oocooooo  ONOONO 


II 


Fuel  Value 
per  Pound 


OOOOOOCO 


. 


-  -^ 


284 


APPENDIX  A 


ill 


•J-1  CJ 

b     -s 


GO      M      H      CM 


i 


<N      CO    <N    OO 


g 


2  M  \q   &  <s 

8    10    ON    C>    fO 


M      <N          M  O         O          O      O       M 


_> 


•S   to  to  O    O  O 

C     H    VO    O      <N  00 

•§     CO    M      M      M  Tf 


OMOOO  1     ^       *°          9 

lO   to    rf    to  •^•M'^-  CO 

tO     H 


o   o   o         oo   o*  co        o     to  ^o   co  o 

H  Tj-      00          CO    <O     M 


OOO      to          cs       O       t>.Qstr) 


1 


§QtoOO  P^°i      P          ^9      ^f011^ 

*°  r^  O    M    ^o          ^  oo      ^~         ^     M      x^»  ^-  10 


fe  W 


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fl  3  -^ 

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rirrfll'i.ll  I  la  I  III 

U3r5     o        >     M^^1     ^,c343^ 
^^W^O       WUU         PQUUU 


APPENDIX  A 


o-  Calor 
Portion 
Measu 


RTION 


!i 

Q 
W 


<s 
I 


O      O      t>-    If) 


10  10  O 

to    <N      M 
00      Tf    Tj- 


OOO 

CO   OO     ON 


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o 


fc 


*    3  £ 


111 


. 


. 


286 


APPENDIX  A 


TABLE  VIII.  — FOODS  or  ANIMAL  ORIGIN 

Important  Ash  Constituents  in  the  One-hundred  Calorie  Portion 
of  Edible  Material » 


*IOO- 

CALORIE 

ASH  ( 

CONSTITUENT 
IOO-CALORIES 

5  PER 

i 

PORTION 
(EDIBLE) 

CaO 

P205 

Fe 

MEATS 
Bacon       

Grants 
16 

Mg. 

I 

Mg. 
4O 

Mg, 

O.2 

Ham 

AA 

5* 

1  80 

I  I 

Beef  lean      .              ... 

co 

420 

3.2 

Veal,  lean      
Chicken                        .     .     . 

65 

Q2 

12 

7 

370 

2  CO 

* 
* 

Frogs'  flesh   

FISH 
Salmon     

153 

40 

42 
c 

670 
2OO 

* 
O.7 

Herring                             .     . 

7O 

CQ 

380 

* 

Halibut     

8« 

IO 

3OO 

O.2 

Pike 

123 

60 

600 

* 

Haddock 

I4O 

40 

c;oo 

* 

Cod 

I  ^O 

21 

600 

06 

DAIRY  PRODUCTS 
Butter      
Cheese                          .     .     . 

13 

22 

3 

2ZO 

4 

22Q 

* 

* 

Cream       . 
Milk                                  .     . 

50 
I41? 

.      70 
230 

IOO 

303 

O.I 
O.3 

Buttermilk    ". 

EGGS 
Whole       , 

280 

68 

415 
60 

610 

240 

* 

1.0 

Yolk                                 .    . 

28 

CQ 

2  7O 

2  3 

White       . 

182 

28 

CO 

O.2 

*  Not  determined. 
JFrom  Sherman,  Chemistry  of  Food  and  Nutrition,  pp.  338-341. 


APPENDIX  A  287 

TABLE  IX.  —  APPROXIMATE  WEIGHTS  OF  ONE  CUPFUL  OF 
COMMON  FOOD  MATERIALS 

Ounces 

Almonds,  shelled ........  5 

Baking  powder 7 

Butter 8 

Beans,  dried 12 

Chocolate,  grated 3! 

Coconut,  shredded .........  3 

Cocoa       ' .     . ,  . .»  4 

Coffee,  ground 3 

Cornmeal 5 

Currants,  Zante 4! 

Farina 5! 

Figs,  dried 4 

Flour,  pastry,  sifted 3! 

Flour,  pastry,  unsifted 4 

Flour,  bread,  sifted 4 

Flour,  bread,  unsifted 41 

Gelatin 4 

Grape  nuts "...  5 

Hominy 55 

Lard 6| 

Lentils ..   , 6| 

Macaroni 4 

Milk .  : 8£ 

Molasses n| 

Oatmeal 6| 

Oats,  rolled  .     .     ..,...,    .    .     .    .    .     .    .     .    .     .  2\ 

Olive  oil 7! 

Peas,  split     . 6£ 

Prunes 6 

Raisins •.    :  4! 

Raisins,  seeded 5f 

Rice 8 

Sugar,  brown .  4! 

Sugar,  granulated 7 

Sugar,  powdered 5^ 

Sugar,  icing 4! 

Sugar,  loaf 4! 

Tea 2 

Tapioca  (pearl) 6 

Walnuts,  shelled 3 


APPENDIX  B 
REAGENTS 

A  mole,  or  gram-molecule,  of  a  substance  is  the  molecular  weight 
in  grams. 

An  equivalent  weight,  or  gram-equivalent,  of  a  substance  is  the 
quantity  which  is  chemically  equivalent  to  one  gram-atom  (1.008 
grams)  of  hydrogen. 

A  molar  solution  of  any  substance  contains  one  mole  of  the 
substance  per  liter.  A  twice-molar  solution  (2  M)  contains  twice 
this  quantity  per  liter,  a  half -molar  solution  (M/2)  half  the  quan- 
tity per  liter,  and  so  on. 

A  normal  solution  of  any  substance  contains  one  equivalent 
weight  of  the  substance  per  liter.  A  twice-normal  solution  (2  N) 
contains  twice  this  quantity  per  liter,  a  half-normal  solution  one 
half  this  quantity  per  liter,  and  so  on. 

EXAMPLES 

HC1          Molecular  weight    36.5 

Mole  36.5  grams 

Equivalent  weight  36.5  grams 

Molar  solution  (M)  contains  36.5  grams  hydrogen 
chloride  gas  per  liter.  This  is  also  the  normal  solu- 
tion (N)  of  hydrogen  chloride. 

A   twice-molar    solution    (2  M,  also  2  N)  contains   73 

grams  hydrogen  chloride  per  liter. 
H2SO4       Molecular  weight       98 

Mole  98  grams 

Equivalent  weight     49  grams 

A  molar  solution  of  sulphuric  acid  contains  98  grams 
pure  sulphuric  acid  per  liter.  This  solution  is  twice- 
normal,  2  N. 

A  half -molar  (M/2)  solution  of  sulphuric  acid  contains 
49  grams  per  liter.     This  is  a  normal  solution. 
288 


APPENDIX  B  289 

A12(SO4)3  Molecular  weight  342. 

Since  there  are  two  atoms  of  aluminium,  each  equiva- 
lent to  three  atoms  of  hydrogen,  the  mole  of  aluminium 
sulphate  is  equal  to  six  equivalent  weights.  The 
equivalent  weight  is,  therefore,  57. 

A  molar  solution  (M)  of  aluminium  sulphate  is  a  six 
times  normal  (6  N)  solution. 

A  normal  solution  (N)  is  one-sixth  molar  (M/6). 


Reagents  for  General  Use 

Acetic  Acid,  2  N.     Dilute  115  cc.  glacial  acetic  acid  to  one  liter. 

Alcohol.     95  per  cent  alcohol,  or  methylated  spirits. 

Ammonium  Chloride,  2  N.     107  grams  to  one  liter. 

Ammonium  Hydroxide,  5  N.  Specific  gravity  0.96.  Dilute 
340  cc.  concentrated  ammonium  hydroxide  (sp.  gr.  0.90)  to  one 
liter. 

Ammonium  Oxalate,  N/2  (M/4).     35  grams  crystals, 
(NH4)2C204 .  H2O,  to  one  liter. 

Barium  Chloride,  N  (M/2).  122  grams  crystals,  BaCl2 .  2  H2O, 
to  one  liter. 

Benzine.     Commercial. 

Calcium  Chloride,  N  (M/2).  56  grams  anhydrous  calcium 
chloride  or  no  grams  crystals,  CaCl2 .  6  H2O,  to  one  liter. 

Calcium  Hydroxide,  Saturated.  Slake  a  lump  of  quicklime, 
weighing  about  half  a  pound,  by  pouring  upon  it  as  much  warm 
water  as  it  will  absorb  and  allowing  it  to  stand  for  about  ten  min- 
utes. Put  the  slaked  lime  in  a  two-liter  bottle,  fill  the  bottle  with 
distilled  water,  and  shake  well,  allow  to  settle,  and  decant  the  clear 
liquid.  By  refilling  the  bottle  with  water  many  batches  of  lime- 
water  may  be  prepared  from  the  same  portion  of  lime. 

Calcium  Sulphate,  Saturated.  About  2.5  grams  crystals, 
CaSO4 .  2  H2O,  to  one  liter. 

Copper  Sulphate,  N/2  (M/4).  62  grams  crystals,  CuSO4. 5  H2O, 
to  one  liter. 

Ether. 

Fehling-Benedict  Solution. 

17.3  grams  copper  sulphate  crystals,  CuSO4 .  5  H2O 
173  grams  sodium  citrate  I  to  one 

100   grams  sodium  carbonate,  anhydrous,  or  270  grams  |    liter 
sodium  carbonate  crystals,  Na2COs .  10  H2O 
u 


2  QO  APPENDIX  B 

Ferric  Chloride,  N  (M/3).  90  grams  crystals,  Feds  .  6  H2O,  to 
one  liter. 

Hydrochloric  Acid,  Concentrated.    About  13  N.    Specific  gravity 

1.20. 

Hydrochloric  Acid,  Dilute,  2  N.  Specific  gravity  1.035.  Dilute 
170  cc.  concentrated  hydrochloric  acid  to  one  liter. 

Iodine.     20  grams  potassium  iodide  1  to  one 
i  gram  iodine  J    liter 

Lead  Acetate,  N  (M/2).  190  grams  crystals,  Pb(C2H302)2 . 3  H2O, 
to  one  liter. 

Litmus.  Heat  10  grams  commercial  cubes  with  about  200  cc. 
water.  Filter.  Wash  the  residue  several  times  with  hot  water. 
Make  up  to  one  liter. 

Magnesium  Chloride,  N(M/2).     102  grams  crystals, 
MgCl2 .  6  H2O,  to  one  liter. 

Mercuric  Chloride,  N/5  (M/io).     27  grams  to  one  liter. 

Millon's  Reagent.  Treat  mercury  with  'twice  its  weight  of 
concentrated  nitric  acid  (in  a  porcelain  dish  under  the  hood). 
Warm  gently  towards  the  last.  When  all  is  dissolved,  add  the 
liquid  to  twice  its  volume  of  water.  Allow  to  settle  a  few  hours 
and  decant  the  clear  liquid. 

Nitric  Acid,  Concentrated.     About  16  N.     Specific  gravity  1.42. 

Nitric  Acid,  Dilute,  2  N.  Specific  gravity  1.065.  Dilute 
130  cc.  concentrated  nitric  acid  to  one  liter. 

Phenolphthalein.  5  grams  in  one  liter  of  alcohol  (or  of  60  per 
cent  alcohol). 

Potassium  Ferrocyanide,  N  (M/4).  106  grams  crystals, 
K4Fe(CN)6 .  3  H2O,  to  one  liter. 

Potassium  Hydroxide,  50  per  cent.     770  grams  to  one  liter. 

Potassium  Iodide,  N/5.     33  grams  to  one  liter. 

Potassium  Permanganate,  M/io.     16  grams  to  one  liter. 

Silver  Nitrate,  N/io.     17  grams  to  one  liter. 

Soap.  Shave  50  grams  white  castile  soap.  Dissolve  in  one 
liter  hot  water  and  filter. 

Sodium  Carbonate,  N  (M/2).  53  grams  anhydrous,  or  143 
grams  crystals,  Na2COs .  10  H2O,  per  liter. 

Sodium  Hydroxide,  30  per  cent.     400  grams  to  one  liter. 

Sodium  Hydroxide,  2  N.  About  85  grams  sodium  hydroxide 
sticks  to  one  liter. 

Sodium  Phosphate,  N  (M/3).     119  grams  crystals 
Na2HP04  .  12  H20  to  one  liter. 


APPENDIX  B  291 

Sulphuric  Acid,  Concentrated.  About  36N(i8M).  Specific 
gravity  1.84. 

Sulphuric  Acid,  Dilute,  2  N.  Specific  gravity  1.065.  Dilute 
59  cc.  concentrated  sulphuric  acid  to  one  liter. 

Reagents  for  Special  Use 

Acetic  Acid,  N.  Experiments  62  and  63.  Dilute  the  reagent 
acetic  acid  to  twice  its  volume;  or  dilute  57.1  cc.  glacial  acetic 
acid  to  one  liter. 

Aluminium  Chloride,  N/2  (M/6).  Experiment  57.  22  grams 
crystals,  Aids  .  6  H2O,  to  one  liter. 

Barium  Acetate,  N/2  (M/4).  Experiment  57.  62  grams  crys- 
tals, Ba(C2H3O2)2  •  H2O,  to  one  liter. 

Barium  Nitrate,  N/2  (M/4).  Experiment  57.  65  grams  to  one 
liter. 

Bleaching  Powder.  Experiments  155-160.  Grind  100  grams 
bleaching  powder  in  a  mortar  and  gradually  add  about  50  cc. 
water,  so  as  to  form  a  paste.  Add  250  cc.  water,  mix  thoroughly, 
and  filter. 

Calcium  Bicarbonate  (Artificial  Hard  Water) .  Experiments  69- 
71.  Dilute  limewater  with  an  equal  volume  of  distilled  water. 
Pass  in  carbon  dioxide  until  the  precipitate  formed  at  first  is  re- 
dissolved.  If  a  little  precipitate  persists,  filter  the  liquid. 

Chromic  Sulphate,  N/2  (M/i2).  Experiment  151.  60  grams 
crystals,  Cr2(SO4)3.  18  H2O,  to  one  liter. 

Copper  Sulphate  for  Fehling's  Solution.  Experiment  98.  17.3 
grams  crystals,  CuSO4 .  5  H2O,  to  one  liter. 

Cyanin.  Experiment  148.  o.i  gram  in  a  mixture  of  50  cc.  al- 
cohol and  50  cc.  water. 

Eisner's  Reagent  (Basic  Zinc  Chloride).     Experiment  132. 
500  grams  zinc  chloride 

20  grams  zinc  oxide 
425  cc.  water 

Warm  until  clear. 

Ferrous  Sulphate,  N/2  (M/4).  Experiment  151.  70  grams 
crystals,  FeSO4 .  7  H2O,  to  one  liter. 

Formic  Acid,  Concentrated.  About  36.5  N.  Experiment  33.  Spe- 
cific gravity  1.22. 

Formic  Acid,  N.  Experiments  62  and  63.  Dilute  37.7  cc.  pure 
formic  acid  (sp.  gr.  1.22)  to  one  liter;  or  dilute  173.6  cc.  formic 
acid  of  sp.  gr.  1.06  to  one  liter. 


2Q2  APPENDIX   B 

Hydrochloric  Acid,  N.  Experiments  62  and  63.  Dilute  the 
reagent  dilute  (2  N)  hydrochloric  acid  to  twice  its  original  volume. 

Hydrochloric  Acid,  3  per  cent.  Experiments  144,  146,  149. 
Dilute  400  cc.  of  the  reagent  dilute  (2  N)  hydrochloric  acid  to 
one  liter. 

Hydrochloric  Acid,  0.4  per  cent.  Experiment  116.  55  cc. 
dilute  (2  N)  hydrochloric  acid  to  one  liter. 

Indigo  Carmine.  Experiment  164.  i  gram  indigo  carmine  to 
one  liter. 

Lowe's  Reagent.  Experiment  154.  Dissolve  25  grams  copper 
sulphate  and  12  cc.  gylcerol  in  250  cc.  water.  Add  just  sufficient 
sodium  hydroxide  solution  to  redissolve  the  precipitate  formed. 

Oxalic  Acid,  Saturated.  1 20  grams  crystals,  H2C2O4 .  2  H2O, 
to  one  liter. 

Oxalic  Acid,  5  per  cent.  Experiments  146  and  149.  50  grams 
crystals  H2C2O4 .  2  H2O  to  one  liter. 

Pepsin.  Experiment  116.  o.i  gram  commercial  dry  pepsin 
to  one  liter. 

Potassium  Chloride,  N/2.  Experiment  57.  37  grams  to  one 
liter. 

Potassium  Bichromate,  N  (M/6).  Experiment  169.  49  grams 
to  one  liter. 

Potassium  Hydroxide,  30  per  cent.  Experiment  32.  385 
grams  to  one  liter. 

Potassium  Hydroxide,  5  per  cent.  Experiment  153.  50  grams 
to  one  liter;  or  dilute  the  50  per  cent  solution  to  15  times  its 
volume. 

Potassium  Hydroxide  in  Alcohol.  Experiment  82.  100  grams 
to  one  liter  alcohol. 

Potassium  Sulphate,  N/2  (M/4).  Experiment  57.  44  grams  to 
one  liter. 

Richardson's  Reagent.  Experiment  154.  Dissolve  25  grams 
nickel  sulphate  crystals,  NiSO4 .  7  H2O,  in  500  cc.  hot  water. 
Precipitate  with  sodium  hydroxide  solution.  Wash  thoroughly 
by  settling  and  decantation.  Dissolve  in  125  cc.  concentrated 
ammonia  (sp.  gr.  0.90)  and  make  up  to  250  cc.  with  water. 

Rosolic  Acid.  Experiment  147.  0.5  gram  in  a  mixture  of  50  cc. 
alcohol  and  50  cc.  water. 

Silver  Sulphate,  Saturated.     7  grams  to  one  liter. 

Sodium  Bisulphite,  30  per  cent.  Experiment  168.  385  grams 
to  one  liter. 

Sodium  Bisulphite,  M.     Experiments  157,  158,  and  164.     104 


APPENDIX  B  293 

grams  to  one  liter;  or  dilute  the  30  per  cent  solution  to  three 
times  its  volume. 

Sodium  Carbonate,  i  per  cent.  Experiment  116  and  144. 
10  grams  anhydrous  sodium  carbonate  to  one  liter ;  or  dilute  the 
reagent  N.  sodium  carbonate  solution  to  five  times  its  volume. 

Sodium  Carbonate,  0.05  per  cent.  Experiment  153.  Dilute  the 
reagent  sodium  carbonate  to  100  times  its  volume. 

Sodium  Chloride,  5  per  cent.  Experiments  57  and  109.  50 
grams  to  one  liter. 

Sodium  Citrate.     Experiment  98.     173  grams  to  one  liter. 

Sodium  Sulphate,  N/2  (M/4).  Experiment  57.  80  grams 
crystals,  Na2SO4 .  10  H2O,  to  one  liter. 

Sodium  Potassium  Tartrate  for  Fehling's  Solution.  Experiment 
98.  346  grams  crystals,  NaKC4H4O6  .  4  H2O,  to  one  liter. 

Sodium  Thiosulphate,  M./2.  Experiment  157.  124  grams 
crystals,  Na2S2O3 .  5  H2O,  to  one  liter. 

Trypsin.  Experiment  116.  o.i  gram  commercial  dry  trypsin 
to  one  liter. 


APPENDIX  C 
THE  METRIC  SYSTEM 
Meanings  of  the  Prefixes 

Milli-  =  one-thousandth,  .001.  Compare  mill  =  one  one- 
thousandth  of  a  dollar. 

Centi-  =  one-hundredth,  .01.  Compare  cent  =  one  one- 
hundredth  of  a  dollar. 

Deci-  =  tenth,  .1.     Compare  dime  =  one  tenth  of  a  dollar. 

Deca-  =  ten,  10.     Compare  decalogue  =  ten  commandments. 

Hecto-  =  one  hundred,  100.  Compare  hectograph  =  a  gelatin 
pad  for  multiplying  copies  of  a  writing  or  drawing. 

Kilo-  =  one  thousand,  1000. 

Length 

10  millimeters  (mm.)  =  i  centimeter  (cm.) 
10  centimeters  =  i  decimeter  (dm.) 

10  decimeters  =  i  meter  (m.) 

1000  meters  =  i  kilometer  (km  ) 

Area 

100  square  millimeters  (mm.2)  =  i  square  centimeter  (cm.2) 
100  square  centimeters  =  i  square  decimeter  (dm.2) 

100  square  decimeters  =  i  square  meter  (or  centare)  (m.2) 

100  square  meters  =  i  are  (a.) 

100  ares  =  i  hectare  (ha.) 

Volume  (Capacity) 

1000  cubic  millimeters  (mm.3)  =  i  cubic  centimeter  (cm.3  or  cc.) 
1000  cubic  centimeters 

(milliliters)  =  i  liter 

1000  liters  =  i  cubic  meter  (or  stere)  (m.3) 

294 


APPENDIX  C  295 


Weight 

10  milligrams  (mg.)  =  i  centigram  (eg.) 
10  centigrams  =  i  decigram  (dg.) 

10  decigrams  =  i  gram  (g.) 

1000  grams  =  i  kilogram  (kg.) 

i  gram  is  the  weight  of  i  cubic  centimeter  of  water  at  4°  C. 

i  kilogram  is  the  weight  of  i  liter  of  water  at  4°  C. 


TABLES   OF  EQUIVALENTS 
Length 

i  millimeter  =      .0394  inch  =  about  ^V  inch 

i  centimeter  =      .394  inch  =  about  f  inch 

i  decimeter    =    3.94  inches  =  nearly  4  inches 

i  meter  =  39.37  inches  =  about  it^  yards 

i  kilometer    =      .62  mile  =  about  f  mile 

i  inch  =  2.54  centimeters  =  about  2\  centimeters 

i  foot  =  3.05  decimeters    =  about  30  centimeters 

i  yard  =  9.15  decimeters    =  about  f£  meter 

i  mile  =  1.61  kilometers    =  about  if  kilometers 


Area 

i    centare    (square   meter)  =1550   square  inches  =  about 
;quare  yards, 
i  hectare  =  2.47  acres  =  nearly  2§  acres. 


Volume 

i  cubic  centimeter  (milliliter)  =      .06  cubic  inch 

10  cubic  centimeters  (i  centiliter)  =      .61  cubic  inch 

100  cubic  centimeters  (i  deciliter)  =    6.10  cubic  inches 

i  liter  =  61.03  cubic  inches 

i  cubic  inch  =  16.39  cubic  centimeters 


296  APPENDIX  C 

Capacity 

1.  Dry  Measure 

i  liter  =  .908  quart 

i  hectoliter  =  2.84  bushels 
i  quart         =  i.io  liters 
i  gallon        =  4.40  liters 
i  bushel       =    .35  hectoliter 

2.  United  States  Liquid  Measure  (Wine  Measure) 

i  liter  =  1.057  quarts 

i  fluid  ounce  =  TV  pint  =  29.6  cubic  centimeters 

i  quart  =  .946  liter 

i  gallon  =3-79  liters 

i  United  States  gallon  =  231  cubic  inches  =  almost  exactly 
the  capacity  of  a  cylinder  7  inches  in  internal  diameter  and  6  inches 
in  height. 

3.  British  Imperial  Liquid  Measure 

i  liter  =  .881  quart  =  about  if  pints 

i  fluid  ounce  =  ^V  pint        =28.4  cubic  centimeters 
i  quart  =  1.135  liters 

i  gallon  =  4.54  liters 

i  Imperial  gallon  =  277.274  cubic  inches  =  the  volume  of  10 
pounds  of  water  at  62°  F.  (about  16°  C.). 

Weight 

i  gram  =  15.43  grains 

i  kilogram  =    2.20  pounds 

i  ounce  Avoirdupois   =  437.5  grains  =    28.4  grams 

i  pound  Avoirdupois  =   7000  grains  =  453.6  grams 


INDEX 


All  acids  are  indexed  under  the  word   "  acid,"   all  alcohols  under  the  word 
"  alcohol,"  all  enzymes  under  the  word  "ferments"  and  all  oils  under  the  word  "  oil." 


Absorption  of  food,  201 

Acetone,  167 

Acetylene,  78 

Acid,  acetic,  85,  86,  114,  115,  116, 
140;  boracic,  see  boric;  boric, 
40,  234 ;  butyric,  85 ;  carbolic,  60, 
234»  256;  carbonic,. 5,  122;  citric, 
85 ;  ferrocyanic,  261 ;  formic,  49, 
50,  114,  116;  hippuric,  194;  hydro- 
chloric, 84,  114,  115,  116,  228,  232, 
245,  261;  hydrofluoric,  84,  228; 
hypochlorous,  244,  245  ;  lactic,  85  ; 
malic,  85;  nitric,  84,  86,  87,  232; 
nitrous,  258;  oleic,  115,  119,  139, 
141;  oxalic,  113;  palmitic,  115, 
119,  139,  140;  phosphoric,  199; 
phytic,  199;  rosolic,  237;  salicylic, 
234;  stearic,  115,  119,  139,  140; 
sulphurous,  244,  245-251 ;  tannic, 
264;  tartaric,  85,  87 

Acid  anhydrides,  169 

Acid  radicles,  86,  88 

Acid  salts,  88 

Acids,  82-85,  86;  ajnino,  182-184, 
1 88;  effect  on  litmus,  82,  84;  fatty, 
139,  264 ;  in  metal  polishes,  107 ; 
ionization  of,  103,  116;  organic, 
84,  140;  reaction  with  alcohols, 
138,  139;  reaction  with  bases  and 
basic  oxides,  98-100;  reaction  with 
metals,  82-85  J  strong  and  weak,  115 

Acrolein,  146 

Air,  24,  80 

Alanine,  183,  184 

Albuminoids,  188,  191 

Albumins,  188 

Alcohol,  amyl,  134;  butyl,  134;  de- 
natured, 67;  ethyl,  67,  134,  136; 
grain,  67,  134,  138;  methyl,  67, 
134, 137  5  propyl,  134 ;  wood,  67,  134 


Aldehydes,  167 

Aldoses,  166—167 

Alizarin,  256,  263,  264 

Alkali,  free,  in  soaps,  120,  148,  149, 
222-223;  volatile,  131 

Alkali  blue,  252 

Alkalies,  91-93 ;  caustic,  93 ;  strong, 
93 ;  mild,  93 ;  weak,  93 ;  fixed,  131 ; 
volatile,  130 

Alkaloids,  182 

Alkanet,  256 

Almond  paste,  276 

Almonds,  276,  279,  287 

Aluminium,  injured  by  free  alkali,  148 ; 
mordants,  263,  264;  polish  for,  108; 
tarnish  of,  105 ;  valence  of,  88 

Amides,  182 

Amines,  183 

Amino  acids,  182—184,  I88,  213 

Amino  radicle,  183,  257 

Ammonia,  127-131,  183,  223;  an- 
hydrous, 128;  "crystal,"  131; 
"household,"  130;  in  metal  polishes, 
107;  liquid,  128;  "solid  household," 

131 

Ammonium  radicle  and  salts,  130-131 
Amyl,  132 
Amyl  acetate,  138 
Amylopsin,  176,  204,  206 
Analysis,  chemical,  24 
Anhydrides,  acid,  169 
Aniline,    135,    183,    256,    260;    aniline 

dyes,  256;   aniline  black,  260-261 
Anion,  103 
Anthracene,  256 
Anthracite,  64 

Antimony,  use  in  dyeing,  265-266 
Apples,  210,  271,  278 
Aqua  ammoniae,  127 
Archil,  256 


?97 


298 


INDEX 


Arrowroot,  177,  273 

Asbestos,  3 

Ashes,  59,  61,  64,  65;  coal,  64;  wood, 

61-62;      of    foods,     163-164,     193, 

278-279,  286;  of  silk,  228 
Asparagine,  182 
Atomic  weights,  31,  33 
Atoms,  20-33 

Bacon,  142,  280,  286 

Baking  powder,  35~37>  287 

Bananas,  207,  268,  269,  271,  278 

Barley,  274,  279 

Bases,  definition,  94,  130;  reaction 
with  acids,  98-100;  ionization  of, 
103,  116;  relation  to  basic  oxides, 
95—96 ;  strong  and  weak,  115 

Basic  oxides,  95,  96;  reaction  with 
acids,  100 

Bass,  283 

Beans,  210,  212,  217,  273,  279,  287 

Beef,  214,  217,  281,  282,  286 

Beets,  210,  272,  278 

Benzaldehyde,  167 

Benzene,  159,  160,  256 

Benzine,  57,  66,  133,  159,  160,  161 

Beriberi,  199 

Bile,  1 60,  199,  204 

Biuret,  187 

Blackfish,  283 

Bleaching,  243-251 ;  by  hydrogen 
peroxide,  248,  251 ;  by  oxidation, 
243;  by  potassium  permanganate, 
249 ;  by  sodium  hypochlorite,  247 ; 
by  sodium  perborate,  249;  by  sul- 
phurous acid,  244;  by  sunlight,  243, 
249 ;  grass,  243,  246,  249 ;  of  cotton 
and  linen,  246;  of  feathers,  248; 
of  ivory,  248;  of  silk  and  wool, 
251 

Bleaching  powder,  244-247 

Blood,  193,  199,  201 

Blueing,  251-253 

Bones,  193 

Borax,  92,  124,  223;  in  soap,  153 

Bran,  199 

Brass,  106,  107,  108 

Bread,  composition  and  nutritive  value, 
211,  275,  279;  formation  of  dextrin 
in,  179;  raising  of,  175 

British  thermal  unit,  52 

Bronze,  106,  107 


Burner,  Argand,  79;    Bunsen,   2,  79; 

Tirrill,  3 
Butter,  139,  141,  284,  286,  287;  cocoa, 

209;  peanut,  276 
Butter  crackers,  275 
Buttermilk,  213,  215,  284,  286 
Butternuts,  210,  276 
Butyl,  132 

Cabbage,  272,  279 

Caffein,  182 

Cakes,  275 

Calcium,  18;  as  a  food  constituent, 
193,  211,  212,  216,  217;  excretion 
of,  in  feces,  194;  in  animal  foods, 
216,  217;  in  vegetable  foods,  211, 
212;  ion  in  hard  water,  121;  ion, 
reaction  with  soap,  121;  valence 
of,  87 

Calcium  bicarbonate  in  hard  water, 
122-125 

Calcium  carbonate,  14,  29-30;  rela- 
tion to  hardness  of  water,  122—125 

Calcium  chloride,  234 

Calcium  hydroxide,  93,  96 

Calcium  hypochlorite,  243,  244—247 

Calcium  oxide,  14,  96 

Calcium  phosphate  in  bones,  193 

Calcium  sulphate,  relation  to  hardness 
of  water,  122-125 

Calico  printing,  266 

Calomel,  88 

Calorie,  definition  of,  52 

Calorimeters,  52,  55;  animal,  195; 
respiration,  195—196 

Candles,  75,  76;  experiments  with, 
43-46 

Caramel,  181 

Carbohydrates,  162,  164,  166-181 ; 
classification  of,  168;  composition 
of,  165;  diffusibility  of,  201-203; 
fuel  value  of,  197;  hydrolysis  of, 
166,  171-172,  203;  oxidation  prod- 
ucts of,  194;  prominence  in  vege- 
table foods,  209;  rarity  in  animal 
foods,  213 

Carbon,  17,  18;  an  element  of  fuels, 
59;  an  element  of  limestone,  19; 
combustion  of,  16,  17,  46;  filaments 
in  electric  lighting,  80-8 1 ;  in  lumi- 
nous flames,  77;  in  organic  com- 
pounds, 132 


INDEX 


299 


Carbonizing,  221 

Carbon  dioxide,  formula  of,  27,  29,  38 ; 
limewater  test  for,  5 ;  production 
from  limestone,  18,  29-30;  produc- 
tion in  combustion,  17,  46-47;  pro- 
duction in  the  body,  194;  produc- 
tion from  marble,  13-14 ;  production 
in  yeast  fermentation,  5 ;  reduction 
to  monoxide,  48 

Carbon  monoxide,  formula  of,  27,  29, 
38;  formation  and  properties,  47- 
50 ;  in  coal  gas  and  water  gas,  59,  69 

Carbon  tetrachloride,  160,  161 

Carboxyl  radicle,  140,  183 

Carrots,  210,  272,  279 

Casein,  184,  185,  216,  238 

Caseinogen,  185 

Catechu,  226,  265 

Cation,  103 

Cauliflower,  212,  273,  279 

Celery,  212,  273,  279 

Cellulose,  168 170.  Ji72.  i8of  2og, 

229-232;  behavior  in  digestion, 
i So;,  esters  of,  232;  hydration  of 
in  mercerizing,  234 ;  in  textile  fibers, 
229,  231-234,  237;  in  vegetable 
foods,  209 ;  nitration  of,  232  ;  solvents 
for,  231-232,  238-240 

Cereals,  200,  212,  273-275,  279 

Cerium,  79 

Chalk,  122;  French,  160 

Charcoal,  see  also  carbon,  41 ;  as  fuel, 
59,  64 

Chardonnet  artificial  silk,  239 

Cheese,  213,  215,  284,  286 

Chemical  changes,  4,  9,  27,  30 

Chemicking,  246 

Chemistry,  subject  matter  of,  i,  2,  9, 
10,  24 

Cherries,  271,  278 

Chestnuts,  276,  279 

Chicken,  281,  286 

Children,  foods  suitable  for,  212,  217 

Chloride  of  lime,  see  bleaching  powder 

Chlorine,  18,  .19,  21,  88,  244,  245 

Chloroform,  160 

Chocolate,  209,  211,  276,  287 

Cholesterol,  220 

Chrome  yellow,  255 

Chromium  oxide,  255 

Cider,  5 

Citrons,  271 


Clams,  213,  285 

Clay,  china,  234 

Coal,  42,  59,  62-65 

Coal  oil,  66 

Cochineal,  256 

Cocoa,  210,  211,  276,  287 

Cocoa  butter,  209 

Coconuts,  276,  287 

Cod,  215,  283,  286 

Coffee,  287 

Coke,  41,  59,  64,  68 

Collagen,  191 

Collodion,  233,  239 

Colloids,  178,  201,  203 

Compounds,  22—25,  38;  nomenclature 
of,  25,  39 

Conduction  of  electricity,  20,  100;  of 
heat,  20 

Cookies,  275 

Combination,  n,  15-17 

Combustion,  41-58^  heat  of,  54;  im- 
portance of,  41;  of  charcoal,  16, 
17;  products  of  incomplete,  47; 
products  of,  8,  46-47 ;  propagation 
of,  56 ;  relation  to  heat,  51—58 ;  spon- 
taneous, 57-58;  surface,  71 

Copper,  1 6,  106;  alloys  of,  106;  car- 
bonate, 106;  hydroxides,  94,  95, 
170;  oxides,  39,  95,  169;  sulphate, 
243 ;  tarnishing  of,  106 

Cornmeal,  274,  279,  287 

Corrosive  sublimate,  88 

Cotton,  229-235;  as  typical  cellulose, 
170,  171,  1 80,  231 ;  boiling-off  of, 
230;  distinction  from  linen,  236- 
238;  dyeing,  257;  fibers,  230; 
mercerization  of,  233 ;  mercerized, 
distinction  from  silk  and  lustra- 
cellulose,  241 ;  plant,  229  ;  printing, 
266 ;  separation  from  silk  and  wool, 
241;  sizing  of,  234;  use  in  gas 
mantles,  79 

Crackers,  275 

Cream,  213,  215 

Cream  of  tartar,  see  potassium  bi- 
tartrate 

Creatine,  182 

Creatinine,  182,  194 

Cresols,  234,  256 

Crystalloids,  178,  203 

Cucumbers,  272,  278 

Cudbear,  256 


300 


INDEX 


Cuprammonium,  or  cuprate,  artificial 

silk,  239 

Cupric  hydroxide,  95 
Cupric  oxide,  95 
Cuprous  oxide,  39,  95,  169 
Currants,  red,  180;  Zante,  271,  278,  287 
Cutch,  226 
Cyanogen,  74 

Dairy  products,  284,  286 

Dalton,  John,  28 

Dandelion  greens,  272 

Dates,  268,  271,  278 

Decay,  15 

Decomposition,  n,  14,  15,  18,  28;    of 

proteins,  185 

Definite  proportions,  law  of,  34 
Deflagrating  spoon,  54 
Dextrin,  168,  172,  179,  234 
Dextrose,  see  glucose 
Diamond,  53 
Diazonium  salts,  258,  262 
Diazotizing,  258 
Dietary  standards,  210,  211 
Digestion,  201-206 
Digestive  fluids,  204 
Disaccharides,  168,  171,  172,  175-177, 

203 

Doughnuts,  274 

Dressing  of  cotton  goods,  234-235 
Dressing  of  linen  goods,  238 
Dry-cleaning,  160,  161 
Dunging,  263 
Dyeing,  254-266 
Dyes,,  acid,  257,  265;  adjective,  255; 

anTline,     256 ;      basic,     257,     265  ; 

"bleeding"  of,   257;    coal-tar,   256; 

developed,    257,    259—262 ;     direct, 

257;    inorganic,  255;    natural,  255; 

organic,    255 ;     mordant,    255,    257, 

263-264;  substantive,  255,  257-259; 

sulphur,  259 ;  synthetic,  256 ;  vat,  259 

Edestin,  189 

Eels,  215,  283 

Eggs,  215,  217,  285,  286;  albumin  of, 
185,  186,  189;  as  food  for  children, 
217;  ash  constituents  of,  217,  286; 
composition  and  nutritive  value  of, 
285;  white  of,  coagulation  of,  185, 
189,  composition  of,  200,  213,  215; 
yolk  of,  191,  216 


Electric  lighting,  80-81 

Electrolysis,  12,  13,  14,  101 

Electrolytes,  100-104 

Electrons,  32 

Elements,  18-21,  29,  32;   symbols  of, 

26,  33 ;  atomic  weights  of,  31,  33 
Emulsion,  159 
Enamelware,  in 
Enzymes,  see  ferments 
Equations,  27 
Equivalent  weight,  288 
Erepsin,  204 
Esters,    138-147;  hydrolysis  of,   143- 

144 ;     saponification    of,     144-145 ; 

"mixed,"  141 ;  of  cellulose,  232 
Ethane,  133 
Ether,  159,  160 
Ethyl,  132 
Ethyl  acetate,  138;  structural  formula 

of,  140 

Ethyl  alcohol,  67,  134,  138 
Ethylamine,  183 
Explosion,   56,   57;  of  acetylene,     78; 

of  kerosene  lamps,  76-77 
Extractives  of  meat,  182 

Fabrics,  the  cleaning  of,  160;  see  also 
fibers 

Farina,  287 

Fats,  composition  of,  165,  285;  con- 
stitution of,  139—142 ;  saponifica- 
tion of,  145—147;  solvents  for,  159— 
1 60;  emulsification  of,  159;  as 
food  constituents,  162-165;  oxida- 
tion products  of,  194;  fuel  value 
of,  197;  digestion  and  absorption 
of,  203,  204 ;  in  vegetable  foods,  211 ; 
in  animal  foods,  213—215;  phos- 
phorized,  216;  in  cotton  dressings, 
234 ;  unsaponified,  in  soaps,  148-149 

Feces,  194,  197 

Fehling-Benedict  solution,  169,  170 

Fehling's  solution,  169,  170 

Fermentation,  alcoholic,  5,  67,  175; 
digestive,  203—206 

Ferments,  143,  206;  amylases,  176, 
178,  204;  amylopsin,  204;  diges- 
tive, 203;  erepsin,  204;  invertases, 
see  sucrases;  lactase,  177,  204; 
lipases,  143,  204;  maltases,  176, 
204;  nature  of,  206;  pectinase, 
235 ;  pepsin,  185,  204,  205,  206;  pro- 


INDEX 


3OI 


teases,  204,  205 ;  ptyalin,  204,  205 ; 
rennin,  185;  steapsin,  144,  204; 
sucrases,  175,  204;  table  of,  204; 
trypsin,  185,  204,  205;  zymase,  175 

Ferric  ferrocyanide,  226,  253 

Ferric  hydroxide,  94,  95,  no,  253,  255 

Ferric  oxide,  95,  109—110,  255 

Fertilizer,  62 

Fiber,  crude,  180 

Fibers,  textile,  218-242;  animal,  218- 
228;  cotton,  229-235;  effect  of 
dyes  upon,  254-255;  hair,  218,  219; 
linen,  235-238;  lustracellulose,  238- 
239;  mineral,  218;  silk,  223—228; 
vegetable,  229—242;  wool,  218—223 

Fibrin,  185,  205 

Fibrinogen,  185 

Fibroin,  223,  224 

Figs,  271,  278,  287 

Filberts,  276 

Fillers  in  soaps,  153 

Filter,  folding,  6,  7 

Finishing  of  cotton  goods,  234 

Fish,  215,  216,  283,  286 

Flame,  41,  42 

Flax,  235,  236,  237 

Flounder,  283 

Flour, wheat,  1 90,210,  234,  274,279,  287 ; 
graham,  212,  274,  279;  rye,  274,  279. 

Foods,  absorption  of,  201 ;  animal, 
213-217,  280-286;  as  building 
material,  192 ;  as  fuel,  193 ;  as 
physiological  regulators,  198;  baked, 
274-275;  digestion  of,  192-199; 
functions  of,  192-199;  general 
composition  of,  162-165;  vegetable, 
207—212,  271—279;  weights  of  one 
cupful  of  common,  287 

Foodstuffs,  inorganic,  162-164,  J93, 
199;  organic,  162,  164,165,  166-199 

Formaldehyde,  167,  257,  259 

Formulas,  26,  27,  29;  structural,  136 

"Fountain  apparatus,"  129 

Fowl,  281 

Frogs'  legs,  216,  285,  286 

Fructose,  167,  168,  173,  213 

Fruit-juice,  fermentation  of,  5,  134; 
sugars  of,  173  ;  pectin  of,  180 

Fruits,  175,  198,  200,  209,  271,  272,  278 

Fruit  sugar,  see  fructose 

Fuels,  59-71;  gaseous,  68-71;  liquid, 
66-68;  solid,  60-65 


Fuel  values  of  nutrients,  197 
Fuller's  earth,  160 
Fungi,  273,  279 
Fustic,  256 

Galactans,  174 

Galactose,  168,  174 

Gallnuts,  265 

Gas,  acetylene,  77,  78;  air,  70;  Blau, 
71;  coal,  42,  59,  68,  77 ;  compressed, 
70;  enrichment  of,  70;  gasoline, 
70,  77;  illuminating,  42,  68-71, 
77-78;  liquefied,  70;  natural,  68, 
78;  oil,  70,  77;  water,  69-70,  78 

Gases,  elementary,  19,  21;  as  fuels,  59 

Gas  mantles,  75,  78 

Gasoline,  57,  66,  133,  159 

Gasoline  gas,  70 

Gastric  juice,  199,  204 

Gelatin,  184,  191,  213,  228,  234,  238, 
285,  287 ;  silk,  see  sericin 

Germ  of  cereals,  211 

Glass,  manipulation  of,  3,_4,_5 

Gliadin,  184,  190 

Globulins,  189 

Glucose,  1 68,  173;  commercial,  173; 
fermentation  of,  by  yeast,  5;  in 
fruit  juices,  5;  in  honey,  213;  in 
silk -weighting,  227. 

Glue,  191,  228 

Glutelins,  190 

Gluten,  190 

Glutenin,  190 

Glycerin  (see  also  glycerol),  147, 155,  234 

Glycerol,  135 ;  an  alcohol,  135 ;  a 
product  of  soap  making,  147 ;  de- 
composition of,  146;  structural  for- 
mula of,  137 

Glyceryl  radicle,  135 

Glyceryl  oleate,  see  triolein 

Glyceryl  palmitate,  see  tripalmitin 

Glyceryl  stearate,  see  tristearin 

Glycine,  183,  184 

Glycogen,  168,  172,  179,  216 

Gold,  106 

Goldbeater's  skin,  202,  203 

Goose,  281 

Gram-equivalent,  288 

Gram-molecule,  288 

Grape  nuts,  287 

Grapes,  271,  278 

Graphite,  53,  no 


302 


INDEX 


Grass  bleaching,  243,  246 
Gums,  234 
Gun-cotton,  233 
Gypsum,  122,  234 

Haddock,  215,  283,  286 

Hair,  191,  218-219 

Halibut,  283,  286 

Ham,  280,  282,  286 

Hardness  of  water,  121—126;  degrees  of, 

125;  permanent  and  temporary,  1 23 
Heat,  51-52;    of  combustion,  54-56; 

produced  in  chemical  reactions,  9; 

production  in   the  body,    193-198; 

units,  52 
Helium,  73 

Hemoglobin,  47,  184,  193,  216 
Hemp,  229 
Herring,  283,  286 
Hexoses,  167 
Hickory  nuts,  276 
Hilum  of  starch  granules,  178 
Hominy,  274,  287 
Honey,  166,  173,  213,  277,  285 
Horse-chestnut  tannin,  265 
Human  body,  composition  of,  192 
Hydrocarbon  radicles,  132 
Hydrocarbons,  108,  133 
Hydrogen,  13,  18,  19,  21,  31,  37;  an 

element  of  fuels,  59 ;  as  a  product  of 

electrolysis,   101 ;    in   acids,   84-86 ; 

ion,  103 

Hydrogen  peroxide,  38, 243, 248-249, 25 1 
Hydrolysis,  of  salts,  117-119,  228;  of 

esters,   143-145;    of  carbohydrates, 

171-172;     of    organic    nutrients    in 

digestion,  203-206;    of  starch,  172, 

i73,    178;     of    stannic   chloride    in 

weighted  silk,  228 
Hydroxides,  94 
Hydroxyl,  101,  103 
Hygroscopicity   of    cotton,    222,  238; 

of  linen,  238;  of  silk,  224;  of  wool, 

221-222 

Ice  colors,  262 
Ignition  temperature,  53 
Illumination,  72-81 
Incandescence,  43,  71-75,  78,  80 
Incandescent  lights,  75,  79,  80 
Indigo,  250,  252,  253,  255-256,  259 
Indigo  carmine,  250,  251,  252 


Intestinal  juice,  204 

Intestines,  absorption  in,  201 ;  diges- 
tion in,  204 

Inversion  of  sugar,  174 

Invertase,  see  sucrase 

Invert  sugar,  174 

lonization,  100-104,  116 

Ions,  102 

Iron,  as  an  element,  19,  20,  22;  cast, 
109;  combination  with  sulphur,  22- 
23;  effect  of  heating,  3,  4;  excre- 
tion of  in  feces,  194;  galvanized, 
in,  112;  in  animal  foods,  216;  in 
foods,  193,  211,  212,  216;  in  hemo- 
globin, 193,  216;  in  vegetable  foods, 
211,  212;  mold,  112;  oxide,  109— 
110,255;  protection  from  corrosion, 
110-112;  rust,  100-113;  rust  stains, 
iif^iis:  sulphide,  22,  23,  25;  use 
in  silk- weigh  ting,  215-216;  valence 
of,  88;  wrought,  109 

Isinglass,  191 

Isomers,  136 

Japan,  in 
Javel  water,  247—248 
Jelly,  1 80,  181 
Jute,  229 

Keratins,  191,  218 
Kermes,  256 

Kerosene,  66,  76,  133,  160 
Ketoses,  166-167 
Khaki,  255 

Labarraque's  solution,  248 
Lac  dye,  256 
Lacquers,  108,  in 
Lactase,  204 

Lactose,  168,  172,  176,  215 
Lakes,  263 
Lamb,  215,  280 
Lampblack,  75 
Lamps,  75,  77 
Lanolin,  220 
Lard,  139,  141,  285,  287 
Lead,  tarnish  of,  105 
"Lead,"  black,  no;  pencils,  no 
Lecithin,  199 
Legumes,  212,  273,  279 
Legumin,  189 

Lemons,  271,  278;  pectin  of  inner  peel 
of,  1 80 


INDEX 


303 


Lentils,  287 

Lettuce,  273,  279 

Leuco  compounds,  259 

Levulose,  see  fructose 

Light,  72;  electric,  80;  gas,  77 

Lignite,  62 

Lignocellulose,  180,  229 

Lime,  acid  phosphate  of,  89;  chloride 
of,  244;  composition  of,  18;  in 
foods,  see  calcium ;  production  from 
limestone,  13,  18;  slaked,  93;  slak- 
ing of,  14,  96 

Limelight,  78-79 

Limestone,  as  a  cause  of  hardness  of 
water,  122;  decomposition  of,  14, 
18,  29-30;  elements  of,  19 

Limewater,  as  reagent  for  carbon 
dioxide,  5  ;  nature  of,  14,  93 

Linen,  180,  229,  235-238;  dressing  of, 
238;  fibers,  236;  hygroscopicity 
of,  238 ;  tests  for,  236-238 

Lipase,  143,  204 

Liquor  ammoniae,  127 

Litmus,  84 

Liver,  213,  281 

Lobsters,  285 

Logwood,  255 

Lustracellulose,  229,  238-241 

Lymph,  201 

Macaroni,  274,  287 

Macaroons,  274 

Mackerel,  283 

Madder,  256 

Magnesium,  3,  82,  87,  105 ;   excretion 

of  in  feces,  194;   ion  in  hard  water, 

121 

Magnesium  chloride,  227,  234 
Magnesium  sulphate,  25 
Malt,  176 
Maltase,  204 
Malt  extract,  176 
Maltose,  168,  172,  176,  177 
Manila,  229 

Marble,  122;  decomposition  of,  13-14 
Marl,  122 
Marmalade,  181 
Matches,  53,  54 
Matrass,  5 
Matter,  20;  "mineral,"  in  foods,  162, 

164 
Meat,  ash-constituents  of,  286;    com- 


position of,  200,  213-215,  216,  280- 
282 ;  extractives  of,  182 

Mercerization  of  cotton,  233-234 

Mercuric  chloride,  7,  232 

Mercuric  oxide,  n,  14 

Mercury,  14,  18,  19 

Metals,  20;  polishing  of,  107;  polishes 
for,  1 08 ;  relation  to  acids  and  salts, 
82-89;  tarnishing  of,  105-106; 
valences  of,  87 

Methane,  59,  69,  133 

Methyl,  132 

Methylamine,  183 

Methyl  butyrate,  138 

Metric  system,  294 

Milk,  as  a  food  for  children,  217;  ash- 
constituents,  200,  286;  calcium  in, 
216,  286;  carbohydrate  of,  176, 
177,  213;  coconut,  276,  composi- 
tion and  nutritive  value,  284 ;  con- 
densed, 215,  284;  evaporated,  215, 
284 ;  experiments  with,  6,  7 ;  phos- 
phorus in,  216,  286;  powder,  215; 
skim,  213,  215,  284;  weight  of 
cupful,  287;  whole,  215,  284 

Millon's  test,  187 

Mineral  matter,  in  coal,  64;  in  foods, 
161-163,  iQ3.  198;  in  wood,  60;  in 
wool,  220 

Mineral  pigments,  255 

Mixtures,  distinguished  from  com- 
pounds, 22 

Molar  solution,  288 

Molasses,  277,  287 

Mole,  288 

Molecules,  28-31 

Monosaccharides,  166,168, 173-177,  203 

Mordants,  255,  263-264,  265,  266 

Mucins,  184 

Mushrooms,  210,  273,  279 

Mutton,  214,  280 

Naphthalene,  256 
Naphthol  (J3-),  258,  262 
Neutralization,  98 
Nicotine,  182 
Nickel,  106,  m 
Nickel  ware,  in,  112 
Nitrocellulose,  232,  239 
Nitrogen,  19,  21,  24,  59 
Nomenclature,  24,  25,  39,  86 
Non-metals,  20 


3°4 


INDEX 


Normal  solution,  288 

Notation,  chemical,  26,  27,  86-87 

Nucleins,  184  i 

Nutrients,  elementary  composition  of, 
165 ;  fuel  values  of,  197 ;  in  animal 
foods,  213-217;  in  vegetable  foods, 
209-212;  organic,  162,  164-199; 
oxidation  products  of,  194,  199 

Nuts,  209,  211,  276,  279 

Oatmeal,  209,  210,  211,  212,  273,  279, 

287 

Oats,  rolled,  211,  273,  287 
Oil,   castor,   139,    141,    155;   coconut, 

iSS;     cottonseed,    139,    150;     lard, 

76, 139 ;  linseed,  58,  139, 141 ;   olive, 

76, 139, 150,  209,  264,  287;  palmnut, 

150,    155;    pear,  see  amyl  acetate; 

pineapple,     see     methyl     butyrate ; 

turkey-red,  161,  264;   whale,  76 
Olein,  see  triolein 
Oleomargarine,  285 
Olives,  209,  211,  269,  272,  278 
Onions,  272,  278 
Oranges,  180,  210,  212,  271,  278 
Organic   acids,    140;    chemistry,    132; 

compounds,  132  ;  radicles,  132 
Oxidation,  in  the  body,  193—198,  199; 

in  bleaching,  243 ;    slow,  58 
Oxidizing  agent,  243 
Oxgall,  1 60 
Oxycellulose,  246,  247 
Oxygen,  u,  13,  16,  17,  18,  19,  21,  24, 

25,  27,  88 

Oyster  crackers,  275 
Oysters,  213,  285 
Ozone,  249 

Paint,  as  a  protective  coating  for  iron, 

in  ;  drying  of,  58 
Palmitin,  see  tripalmitin 
Pancreatic  juice,  176,  204 
Paper,  229 
Paraffin,      66 ;      hydrocarbons,      133 ; 

wax,  66,  76,  no,  133 
Paranitraniline  red,  262 
Parchment  paper,  201,  202,  232 
Parsnips,  272,  278 
Peaches,  271,  278 
Peanuts,  210,  276,  279 
Pearl  ash,  151 
Pears,  271,  278 


Peas,  210,  273,  279,  287 

Peat,  59,  62 

Pecans,  276 

Pectin,  1 68,  180,  209,  235,  237 

Pentoses,  167 

Pepsin,  185,  204,  205,  206 

Peptides,  183 

Peptones,  185 

Perch,  283 

Persian  berry,  255 

Petrolatum,  66 

Petroleum,  66,  76,  77,  133,  153 

Phenolphthalein,  120 

Phenols,  256 

Phenylamine,  see  aniline 

Phosphorus,  20,  43-44,  53,  54;  ex- 
cretion of,  in  feces,  194;  in  animal 
foods,  216,  217;  in  foods,  193,  199, 
211,  212,  216,  217;  in  proteins,  184, 
216;  in  vegetable  foods,  211,  212 

Phosphorus  pentasulphide,  53 

Physical  change,  3,  9,  29-30 

Physical  states,  20 

Pickerel,  215,  283 

Pickles,  272,  278 

Pies,  275 

Pike,  283,  286 

Platinum,  3,  106 

Plumbago,  see  graphite 

Plums,  271,  278 

Polypeptides,  183 

Polysaccharides,  168, 171, 172,  177-181, 
203 

Pork,  214,  215,  270,  280,  282 

Potash,  see  potassium  carbonate  ; 
caustic,  see  potassium  hydroxide 

Potassium,  18,  20,  87 

Potassium  binoxalate,  89,  113 

Potassium  bisulphate,  89,  146 

Potassium  bitartrate,  35—37,  89 

Potassium  carbonate,  in  commercial 
soaps,  151,  157;  in  wood  ashes, 
61-62 

Potassium  chlorate,  n,  18,  29,  54 

Potassium  chloride,  18,  29 

Potassium  hydroxide,  93 

Potassium  iodide,  7,  8 

Potassium  permanganate,  243,  249,  250 

Potassium  sodium  tartrate,  35 

Potatoes,  209,  211,  272,  278 

Potatoes,  sweet,  272,  278 

Poultry,  281,  286 


INDEX 


305 


Precipitate,  6 

Prefixes,  signification  of,  39,  294 

Prepares,  262 

Primuline,  258 

Printing  of  cotton,  266 

Propyl,  132 

Protein  derivatives,  185 

Proteins,  162,  164,  182-191 ;  as  body 
building  material,  192-193 ;  classes 
of,  184,  188-191 ;  composition  of, 
165;  conjugated,  184;  constitu- 
tion of,  183;  derived,  184;  diges- 
tion of,  203,  204 ;  estimation  of  in 
foods,  182 ;  fuel  value  of,  197 ;  hydroly- 
sis of,  183,  184;  importance  in 
animal  nutrition,  193;  in  animal 
foods,  213-216;  in  vegetable  foods, 
210,  2ii ;  native,  184;  origin  of 
name,  193 ;  oxidation  products  of, 
194-195 ;  tests  for,  185-187 

Proteoses,  185 

Prunes,  271,  278,  287 

Prussian  blue,  226,  253 

Ptyalin,  176,  204,  205 

Pudding,  tapioca,  275 

Pumpkins,  210,  272,  278 

Putty  powder,  107 

Pyroxylin,  233,  239 

Quercitrin  bark,  255 

Quicklime,  see  lime  and  calcium  oxide 

Quinine,  182 

Radicals,  see  radicles 

Radicles,  acid,  86;  amino,  183;  am- 
monium, 130;  amyl,  132;  butyl, 
132  carboxyl,  140,  183;  ethyl, 
132  glyceryl,  135 ;  hydrocarbon, 
132  hydroxyl,  101 ;  organic,  132- 
137  propyl,  132;  sulphate,  101 ; 
valence  of  acid,  88 

Radioactivity,  19,  32 

Radishes,  209,  210,  272,  279 

Raisins,  271,  278,  287 

Ramie,  79,  229 

Raspberries,  271,  278 

Reagents,  288-293 

Reducing  agent,  244 

Reducing  sugars,  170 

Reduction,  49,  169,  244 

Refuse  of  foods,  207,  215 

Retting  of  flax,  235 


Rhubarb,  273,  279 
Rice,  274,  279,  287 
Rolls,  275 

RoOtS,  212,  272,  278-279 

Rosin,  152 

Rottenstone,  107 

Rouge,  107 

Rust,  109-113;  stains,  112-113 

Saccharose,  see  sucrose 

Sago,  177,  277 

Saliva,  176,  199,  204 

Salmon,  215,  283,  286 

Salt,  common,  see  sodium  chloride; 
Epsom,  see  magnesium  sulphate; 
Glauber's,  see  sodium  sulphate; 
of  sorrel,  see  potassium  binoxalate ; 
of  lemons,  see  potassium  binoxalate ; 
Rochelle,  see  potassium  sodium 
tartrate;  smelling,  131 

Salt  colors,  256 

Saltpeter,  22 

Salts,  see  also  salt;  acid,  88;  defini- 
tion of,  86;  hydrolysis  of,  117-119; 
nomenclature  and  notation  of,  86; 
reactions  to  litmus,  118-119;  re- 
lation to  acids  and  bases,  99 ;  relation 
to  acids  and  metals,  85 

Sandalwood,  256 

Saponification,  144-145 

Sardines,  215,  283 

Science,  i 

Scleroproteins,  191 

Scouring  powders,  148,  156 

Sericin,  223,  224 

Shad,  215,  283 

Shad  roe,  213,  216,  285 

Shellac,  108 

Shellfish,  213,  216,  285 

Silk,  223-238;  artificial,  229;  boiled- 
off,  224;  degumming  of,  224;  dis- 
tinction from  wool,  191 ;  ecru,  224  ; 
origin  of ,  2 23  ;  pongee,  223;  "pure," 
227;  separation  from  wool,  225; 
separation  from  cotton,  241-242 ; 
souple,  224;  solvents  of,  225,  242; 
weighting,  225-228;  wild,  223 

Silkworms,  223,  238—241 

Silver,  106,  107,  108 

Silver  chloride,  6,  27,  31 

Silver  nitrate,  6,  27,  31,  35 

Silverware,  106 


306 


INDEX 


Sirup,  corn,  173;  glucose,  173;  maple, 
277 

Sisal,  229 

Sizing  of  cotton,  234 

Smelt,  283 

Smoke,  59 ;  oil  of,  60 

Soap  bark,  160 

Soap  powders,  156 

Soaps,  as  emulsifying  agents,  158-159; 
calcium,  121;  carbonates  in,  151; 
colored,  155;  commercial,  148-157; 
curd,  147;  detergent  effect  of,  159; 
effect  of  water  upon,  119;  effect  of 
hard  water  upon,  121,  125  ;  fillers  in, 
153;  floating,  155;  for  woolens, 
222,  223;  free  alkali  in,  120,  148, 
149;  hard,  119,  147,  150;  hydrolysis 
of,  119;  in  cotton  dressings,  234; 
making  of,  146-147 ;  marine,  155 ; 
medicated,  156;  mottled,  156; 
perfumed,  155;  petroleum  products 
*&>  IS3  J  reaction  with  bleaching 
powder,  247;  rosin,  152;  scouring, 
156 ;  sodium  silicate  in,  152  ;  sodium 
resinate  in,  152;  soft,  119,  147; 
transparent,  155 ;  unsaponified  fat 
in,  148,  149 ;  water  in,  149-150 

Soapwort,  160 

Soda,  baking,  see  sodium  bicarbonate ; 
caustic,  see  sodium  hydroxide; 
washing,  see  sodium  carbonate 

Soda  crackers,  275 

Sodium,  20,  26,  84,  87,  92,  101 

Sodium  bicarbonate,  35-37,  88,  92 

Sodium  bisulphate,  88 

Sodium  bisulphite,  247,250,  251,259,260 

Sodium  ^-naphtholate,  262 

Sodium  carbonate,  36;  in  commercial 
soaps,  151,  156,  157;  use  in  water- 
softening,  124—126 

Sodium  chloride,  257;  electrolysis  of, 
101 ;  preparation  from  sodium  and 
hydrochloric  acid,  84;  reaction 
with  silver  nitrate,  6,  27,  31,  35; 
use  in  dyeing,  257;  use  in  soap- 
making,  147;  use  in  washing  dyed 
cottons,  257 

Sodium  ferrocyanide,  261 

Sodium  hydrosulphite,  259,  260 

Sodium  hydroxide,  92,  93,  101 ;  elec- 
trolysis of,  101 

Sodium  hypochlorite,  243,  247-248 


Sodium  hyposulphite,  247 

Sodium  perborate,  249 

Sodium  peroxide,  249 

Sodium  phosphate,  89,  227 

Sodium  resinate,  152 

Sodium  silicate,  in  soaps,  152;  use  in 
silk- weigh  ting,  227 

Sodium  sulphate,  117,  124,  257,  265 

Sodium  sulphide,  259 

Sodium  thiosulphate,  247 

Solution,  by  chemical  action,  100; 
colloidal,  201-203;  simple,  100;  with 
and  without  ionization,  100 

Soot,  60,  76 

Souring  in  bleaching,  247 

Spectroscope,  73 

Spinach,  212,  273,  279 

Spirits,  methylated,  67  ;  of  hartshorn,  128 

Squashes,  272,  278 

Starch,  166,  168,  171,  172,  177-179, 
209,  234,  235,  277;  animal,  see 
glycogen ;  arrowroot,  273  ;  corn,  273, 
277;  forms  of  granules,  178;  iodine, 
test  for,  171,  178;  in  cotton  dress- 
ings, 234,  235;  soluble,  179 

Steapsin,  144,  204 

Stearin,  see  tristearin 

"Stearin,"  commercial,  76 

Steel,  109 

Stove  polish,  no 

Stoving,  251 

Substances,  9,  20 

Sucrase,  175,  176,  204 

Sucrose,  168,  175;  in  honey,  213 

Suet,  285 

Suffixes,  signification  of,  -ate,  25 ;  -ic, 
39;  -ide,  25;  -ite,  39;  -ous,  39 

Sugar  (cane-sugar),  see  also  sucrose ; 
caramelization  of,  181 ;  decomposi- 
tion of,  12;  elements  of ,  2  2 ;  inversion 
of,  174;  use  in  silk- weighting,  227 

Sugars,  1 66,  168;  barley,  181;  cane, 
see  sucrose  and  sugar;  fruit,  see 
fructose;  grape,  see  glucose;  in- 
vert, 174;  malt,  see  maltose;  milk, 
see  lactose 

Suint,  220 

Sulphur,  16,  19,  20,  26,  27,  249,  250; 
dyes,  259;  in  proteins,  184,  191; 
tarnishing  of  silver  by,  106;  use  in 
bleaching,  251 

Sulphur  dioxide,  250,  251 


INDEX 


307 


Sumac,  264,  265 
Symbols,  26,  29,  33 
Syrup,  see  sirup 

Taffy,  181 

Talc,  234 

Tallow,  75,  139,  141,  150,  155 

Tannins,  225,  264—266 

Tapioca,  177,  274,  275,  277,  287 

Tarnish  of  metals,  105-109 

Tartar,  cream  of,  see  potassium  bi- 
tartrate 

Tartar  emetic,  265 

Tea,  287 

Temperature,  51,  52;  ignition,  53 

Textiles,  chemistry  of,  229-266 

Thermometers,  52 

Thorium,  79 

Tin,  use  in  silk- weighting,  227,  228; 
a  constituent  of  bronze,  106;  as  a 
protective  coating  for  iron,  1 1 1 

Tinware,  in,  112 

Toast,  275 

Tomatoes,  210,  272,  278 

Tongue,  213,  281 

Triolein,  140,  141 

Tripalmitin,  139,  140 

Tristearin,  139 

Trout,  215,  283 

Tryptophane,  184,  213 

Tungsten  filaments,  80-81 

Turkey,  281 

Turkey  red,  256,  264 

Turmeric,  256 

Turnips,  209,  272,  279 

Turpentine,  160 

Tyrosine,  213 

Ultramarine,  252,  253 

Uranium,  31 

Urea,  182,  194,  195,  197 

Valence,  87 

Vaseline,  66,  no 

Vat  dyes,  259 

Veal,  214,  215,  281,  282,  286 

Vegetables,    198,    200,    207-212,  272, 

273,  278,  279 
Venetian  red,  107 
Vermicelli,  274 
Viscose,  239,  240 
Vitellin,  184 


Walnuts,  210,  276,  279,  287 

Water,  electrolysis  of,  12,  13,  30;  ele- 
ments of,  22;  hard,  121-126;  in 
soaps,  149,  150;  in  foods,  162-163; 
in  wool,  222;  production  in  com- 
bustion, 8,  46—47 ;  production  from 
its  elements,  13,  24,  30;  softening 
of,  124 

Water  glass,  see  sodium   silicate 

Watermelons,  268,  271,  278 

Wax,  bees',  76,  138;  Carnauba,  138; 
cotton,  230;  flax,  237;  in  cotton 
dressings,  234;  paraffin,  66,  76, 
no,  133;  spermaceti,  76 

Weights  and  measures,  metric  system 
of,  288-296 

Weights  of  one  cupful  of  food  materials, 
287 

Welsbach  gas  mantles,  79 

Wheat  and  wheat  products,  274,  279 

Whey,  213,  215,  284 

Whitefish,  283 

Whiting,  107,  234 

Wine,  5 

Wood,  41,  59,  60-62,  1 80 

Wood-pulp,  229,  238 

Wool,  218-223,  241,  251,  259,  261  ; 
action  of  alkalies  on,  222,  223; 
bleaching  of,  251 ;  carbonizing  of, 
221;  dyeing  of,  259,  265;  felting 
of,  219;  factors  influencing  quality 
of,  219-220;  grease,  220;  hygro- 
scopicity  of,  221 ;  raw,  220;  scouring 
of,  220;  separation  from  cotton, 
241;  structure  of,  219;  test  for 
sulphur  in,  191 ;  treatment  of,  to 
prevent  shrinking,  246 

Xanthoproteic  test,  186 

Yeast,  fermentation  by,  5,  134.  ^75 

Zein,  184 

Zinc  as  a  protective  coating  for  iron, 

in;   tarnish  of,  105;   a  constituent 

of  brass,  106 
Zinc  chloride,  232,  234 
Zinc  oxide,  243 
Zwieback,  275 
Zymase,  175 


t) 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 


3     6  73 -8PM     9 


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